Solar System Watch

Dusty planetesimal ring orbiting star HR 4796 A

2012-01-04T19:42:00.000-08:00

This image of a circumstellar dust ring was recently acquired by C. Thalmann and colleagues at the 8 meter Subaru telescope that the Japanese operate on the summit of mount Mauna Kea in Hawaii. Although the dust ring is nearly circular, the line-of-sight to the ring is oblique which makes the ring appear elongated. To reveal the faint ring, the astronomers must subtract a model image of the very bright central star, but imperfections in the star-subtraction results in the radial residuals seen in the image. Nonetheless the dust ring is still quite prominent despite those residuals, and its radius is about 80 AU. This dust is thought to be the result of collisions occurring among unseen planetesimals also orbiting within the ring. These planetesimals probably resemble the comets that inhabit our Kuiper Belt, which is the Sun's outermost debris belt that is of radius 45 AU. Another interesting feature of this image is that the dust ring's center is offset slightly from the star. Although the origin of this offset is uncertain, an unseen extra-solar planet is implicated, because its gravitational influence can displace the ring's center. But if there is an exoplanet here, it is too faint to be seen or is obscured by the residual starlight. For more information about this circumstellar dust ring, see this press release.

Planet formation and destruction via gravitational instability

2011-11-30T15:07:00.000-08:00

This graphic shows a computer simulation of a circumstellar disk that orbits a young star, with each snapshot showing the state of the disk 1,500 years later. This disk is gravitationally unstable, which means that the disk's gravitational attraction for itself causes material to contract into spirals that can also clump up further to form Jupiter-mass protoplanets. The black circles in the above (click picture to zoom in) follow one such clump that first forms at a distance of 300 AU (ie 300 times the Sun-Earth distance) from the central star, which then spirals inwards due to its interactions with the disk. This simulation illustrates one of the difficulties in forming giant planets via gravitational instability, since the clumps that do form by this process also tend to get driven inwards by the disk, where they might accrete onto the central star. For additional details, see the preprint by Zhu and colleagues.

Spiral arms in disk suggests unseen planets

2011-10-21T16:04:00.000-07:00

This image of the disk that is in orbit about the young star SAO 206462 suggests that this disk might be perturbed by one or more unseen planets. This image was acquired at the Japenese Subaru telescope in Hawaii by Carol Grady (Eureka Scientific). In this image, the central star is deliberately masked by the telescope's optics, which revealing a broad disk of gas and dust in orbit about the star. The size of this disk is at least twice the diameter of our Solar System. Planets are known to form in these circumstellar disks, and computer simulations of this process show that a young giant planet can also launch spiral density waves in such a disk. So this disk's spiral appearance does suggest that giant planets may have formed here. But keep in mind that this is not the only explanation. For instance, the gravity of passing star can also disturb a disk, and such a disturbance would wind-up over time and also resemble a spiral. But further study of this system may one day reveal whether the disk at SAO 206462 is indeed planet forming. See this press release for more details.

Vesta's rugged surface

2011-10-13T18:56:00.000-07:00

This image is a computerized rendering of what a hypothetical observer migth see when looking obliquely along the mountains and craters on the giant asteroid Vesta. Of course the Dawn spacecraft is in orbit about Vesta, and thus is always looking down upon the asteroid, so Dawn would never see anything like this. But Dawn has now collected enough measurements of Vesta surface topography to assemble a detailed computer model of the asteroid's surface. With that model, one can then calculate the view that any observer might see when looking in any direction about Vesta. Keep in mind that Vesta is only about 700 miles across, so the more distance mountains shown here would not be seen by that observer; they'd lie below the horizon and thus would be hidden. But that computerized view can be adjusted to remove the asteroid's curvature (ie, flatten the asteroid) while preserving its topography, as is seen here. See the Dawn website for more details about this computerized image of Vesta's rugged surface.

Four fascinating videos on science and math

2011-09-18T18:20:00.000-07:00

Last week I was in a working meeting with a number of planetary scientists. When there was a lull in the meeting, I asked everybody to show me their favorite online science videos. Below are the best four, and all are quite remarkable.

The first is called Doodling in Math Class: Snakes and Graphs. This amazing video is by Vi Hart, and she shows how to sketch elaborate doodles that have a mathematical theme. The very clever (and funny) commentary provides tip on how to draw, plus some hints about the mathematics that are associated with each sketch.

The second is a 50 minute video by Astronaut Don Petit, who recorded several of the fluid-dynamics experiments that he performed while in the microgravity environment of the Space Station; see this youtube video. One interesting clip shows an air bubble that he creates inside a floating water bubble, which to me resembles a miniature planet that has a central core and an overlying mantle. He then injects little water bubbles into the air core, which careen around and around the core boundary until getting absorbed explosively by the mantle. Another video segment show how small bodies in the weightless environment of space can collide, merge, and form elaborate dendritic objects. This is in fact how planetesimals, which are the precursors to asteroids and planets, are thought to have formed. A fascinating video.

The next two videos are from the Slo Mo Guys. They use a high-speed camera to record ordinary events that are usually just a blur. Playing their movies very slowly then reveals lots of hidden events that are too fast to be seen by human eyes. In the first video, Giant 6ft Water Balloon, one of the Slo Mo guys leaps onto and breaks a large water-filled balloon. Slow motion video reveals how the entire balloon shivers as inertial waves propagate across the balloon and ultimately rip the balloon to shreds. In very cool slow mo.

But my favorite movie is Droplet Collisions at 5000fps, which provides an excellent analogy for how craters form and develop when an asteroid impacts a planet. Oh, and the Slo Mo guys are hilarious, too.

Earth's first Trojan asteroid

2011-09-06T06:09:00.000-07:00

Earth's first trojan asteroid was recently detected by Martin Conners (Athabasca University) and colleagues using NASA's WISE satellite, which is surveying the sky at infrared wavelengths. Trojans are asteroids that reside in or near two sites that lead or trail a planet's orbit by 60 degrees, and these orbits are stablized by the combined gravities of the Sun, the planet, plus the centrifugal force that is due to the asteroid's orbital motion. This particular asteroid is known at 2010 TK7, and it is small, maybe a half mile across. This Trojan is indicated by the small white dot in the above graphic. The blue dots show the Earth's motion about the Sun, while the green dots show that 2010 TK7's motion can carry it quite far from the stable equilibrium site at 60 degrees, which is also known at the L4 Lagrange point. Indeed, orbit calculations by Paul Wiegert (University of Western Ontario) show that this is only a temporary Trojan, since Earth captured that object at its L4 point about 1500 years ago, and it will probably escape back into interplanetary space in a comparable amount of time. See Wiegert's very nice website on 2010 TK7 for more details.

A pulsar planet with a diamond core?

2011-08-26T08:35:00.000-07:00

PSR J1719−1438 is a pulsar, which is a rapidly spinning neutron star. Such an object is called a pulsar because its powerful magnetic field shoot jets of energetic particles out along its magnetic poles. This also makes the spinning neutron star appear to pulse as its jet sweeps past an astronomer on Earth.

Slight variations in the timing of the neutron star's pulses can indicate the presence of an unseen planet that is also orbiting the pulsar. Indeed, the first known extra-solar planet was discovered via pulsar timing variations. Matthew Bailes (Swinbourne University in Australia) discovered the timing variations in pulsar PSR J1719−1438, and they are due to a Jupiter-mass planet in a very close two-hour orbit about the neutron star. He and his colleagues also show that this planet must be very small and dense to avoid having been ripped apart by the neutron star's gravitational tide. This planet's minimum density is about 20 times that of Jupiter's, and the planet's core is likely made of carbon. If so, then carbon at the center of this very dense planet will have crystallized, possibly into one giant planetary core-sized diamond. See this press release for more details.

Streaks at Martian crater suggest a watery flow

2011-08-13T10:31:00.000-07:00

This is the upper edge of the Newton crater on Mars, imaged my the Mars Reconnaissance Orbiter (MRO). The dark streaks extending downslope are very interesting; they are only seen in spring and summer, and fade away during the colder seasons. These streaks might be due to a flow of subsurface water that is likely a salty brine due to long-term contact with the martian rocks. Salt lowers the freezing point, which might allow subsurface ice to melt and seep down the crater's slope. This might be the cause for the seasonal stains that are seen in the crater's soil. Additional details can be found at the MRO website, including this nice movie of streaks forming and then fading. If these streaks are in fact watery seeps, they will be of great biological interest because wet soil will be a natural place to look for microbial life on Mars.

Vesta is groovy

2011-08-01T09:38:00.000-07:00

The giant asteroid Vesta, as seen by the Dawn spacecraft, which has been orbiting Vesta since July 15. See the Dawn website for more information. This movie of Vesta's rotation is also interesting...evidently, Vesta is quite `groovy'.

Last shuttle re-entry, as seen from Space Station

2011-07-22T08:08:00.000-07:00

Shuttle Atlantis' final return to Earth, as seen from the International Space Station. This picture comes from the NASA Image of the Day.

Hubble finds new moon orbiting Pluto

2011-07-20T06:45:00.000-07:00

Mark Showalter (SETI Institute) just discovered a fourth moon orbiting Pluto, designated P4 for now. It is quite small, about 15 miles across, and its orbit resides between satellites Nix and Hydra. This discovery was quite accidental, because Showalter was observing the Pluto system to look for signs of any planetary rings there; see the Hubble website for more details. Since Pluto seems ripe with satellites, we might expect the New Horizons spacecraft, which flies by Pluto in 2015, to find even more tiny satellites.

Dawn spacecraft to orbit Vesta tonight!

2011-07-15T11:14:00.000-07:00

The Dawn spacecraft goes into orbit about the giant asteroid Vesta tonight, July 15, about 10pm Pacific time or 1am Eastern time July 16. See the Dawn website for more.

Cassini monitors monstor storm on Saturn

2011-07-06T19:30:00.000-07:00

Cassini snapped this picture of a monster storm on Saturn on Feb. 25, 2011. This storm started in December 2010, and has since wrapped itself all the way around the planet, spanning an area about 8 times that of the Earth's total surface. The thin dark band at the equator is Saturn's rings seen edge on, and the broader dark bands below are the shadows cast by the rings.

The image below is color coded to indicate the altitude of the various cloud layers in the storm. Blue, white, and yellow indicate clouds at higher altitudes, with green, red, and brown colors showing clouds that are deeper in this gas giant planet's atmosphere. Check the CICLOPS website for more information and Cassini images of Saturn.

Dawn gets closer Vesta

2011-07-02T11:19:00.000-07:00

The Dawn spacecraft's view of Vesta's rugged surface gets a little sharper as the spacecraft approaches this very large asteroid. Dawn is still 100,000 miles away from Vesta, but it arrives and goes into orbit about that giant asteroid soon on July 16! Meanwhile, keep an eye on the Dawn website for the latest images that will get more dramatic over time as the spacecraft nears.

Helene at Saturn

2011-06-30T19:08:00.000-07:00

The Cassini spacecraft captured this closeup image of Helene on June 18, 2011. Helene is a small satellite of Saturn about 20 miles across. Helene is a coorbital satellite, which means that it shares an orbit with the much larger satellite Dione that is ~30 times larger and ~30,000 times more massive. Helene resides at Dione's L4 Lagrange point, which is a stable niche in Dione's orbit that leads that satellite by 60 degrees. The other stable niche is of course the L5 Lagrange point that trails Dione by 60 degrees. The orbit of a coorbital satellite is analogous to the Trojan asteroids that lead or trail Jupiter by 60 degrees in its orbit about the Sun.

No one knows how a coorbital satellite like Helene came to reside in such a special orbit. But it is conceivable that a coorbital satellite is debris that was excavated when the larger satellite Dione was stuck by a comet long ago. If this scenario is correct, then a lucky fraction of that debris managed to find and settle into one or both Lagrange points where it could have reassembled into a small coorbital satellite like Helene.

To see more images of Helene, as well as the rest of the Saturnian system, visit Cassini's CICLOPS website.

The Dawn spacecraft approaches asteroid Vesta

2011-06-13T10:56:00.000-07:00

The is the Dawn spacecraft's view of the asteroid Vesta. Dawn is the NASA mission that will visit two asteroids, beginning with Vesta in a few weeks, and then Ceres in 2015. Dawn will go into orbit about Vesta on July 16 to study that asteroid's surface for about a year. Vesta is about 300 miles across and is the fourth largest asteroid. Vesta's surface is composed of basaltic rock, or lava, which makes this asteroid quite unique and very interesting. Evidently Vesta was volcanically active in the past, likely when it first formed 4.5 billion years ago.

In July 2012, Dawn will then fire up its ion engine and depart Vesta for its 3 year trip to asteroid Ceres, which is the largest asteroid, one that appears to be quite rich in water. Meanwhile, keep an eye on the Dawn mission website for better pictures of Vesta that will soon get much more interesting when the spacecraft goes into orbit.

Free floating planets might outnumber the stars in the Galaxy

2011-05-18T19:41:00.000-07:00

A recent gravitational microlensing survey indicates that there may be twice as many free floating planets in our Galaxy than stars. Gravitational microlensing is the brightening that occurs when a dim but massive object passes along the line of sight to a more distant brighter object. According to Einstein's theory of relativity, mass bends spacetime, so the path followed by a light ray is deflected (ie lensed) if passing near enough to a star or a planet. So an astronomer observing a lensed star will see it brighten for a month or two if a very dim star (such as a white dwarf or neutron star) passes near the line of sight (LOS). This also occurs if a planet passes near the LOS, but the lower mass planet has a smaller gravitational influence, so the lensing event is briefer, only a few days.

This is illustrated in the above figure, which shows an otherwise steady star brightening by 40% during three days. These planetary microlensing events are quite rare, so astronomers must continuously monitor millions of stars just to detect 10 such microlensing events in one year. From the observed frequency of these microlensing events, it can be shown that most of the lensing objects are free-floating Jupiter-mass planets that are not bound to any star. But this unusual finding is consistent with some models of planet formation, which predict that when multiple planets form around a star, the planets' gravitational interactions can eject one or more planets from the system. Those ejected bodies are free-floating planets, and their fate is to roam the Galaxy unseen, except in these microlensing surveys. These results were obtained by astrophysicists T. Sumi and K. Kamiya (Osaka Japan) and others, with further details reported in their preprint.

Propellers and wakes in Saturn's rings

2011-05-03T11:23:00.001-07:00

This figure shows results from an Nbody simulation of a small patch in Saturn's rings; click figure to zoom in. Small dots represent meter sized ring particles, while the circle at the center is a 150m moonlet that is embedded in the ring. All bodies are travelling to the right as they orbit Saturn, but keep in mind that those nearer Saturn (which is far downwards in this figure) orbit faster, so ring particles in the lower x<0 half of this figure are drifting towards the right side of the moonlight, while those in the upper x>0 half are drifting left of the moonlet. This Nbody simulation was performed by Shugo Michikoshi and Eiichiro Kokubo, and their results are detailed in this preprint.

The upper figure shows what happens in a low mass ring having a surface density of 60 grams/cm^2. As particles drift past the moonlet they receive a kick due to the moonlet's gravity, which in turn opens a propeller-shaped gap in the ring. The Cassini spacecraft has in fact observed many such propellers orbiting in Saturn's A ring, like the one seen below; see the CICLOPS website for more details about this image. Curiously, the model predicts that the propeller should appear as a dark gap in the ring, while the Cassini image below shows that a propeller is bright. The meaning of this is unclear, but it may indicate that the propeller gap is also filled with sunlight-reflecting dust grains that are produced as ring particles collide near the moonlet.

The lower Nbody simulation (in the lower half of the top graphic) shows results for a high mass ring of surface density 400 grams/cm^2. In this case, the higher ring gravity cause the ring particles to condense into ropy or taffy-like structures that are known as wakes. These wakes dominate the ring's appearance and completely wash-out the propeller that the moonlet is trying to form. The fact that propellers are seen in Saturn's A ring, while none have been observed in Saturn's B ring, suggest that the A ring is a relatively low mass ring that allows moonlets to form propellers, while the B ring is massive and full of gravitating wakes that inhibit any such propellers.

Messenger's first image from Mercury orbit

2011-03-29T15:26:00.000-07:00

The planet Mercury acquired its first artificial satellite on March 17, when the Messenger spacecraft went into orbit about the planet. Two weeks later, the spacecraft acquired its first image from Mercury orbit, with 75,000 more images to be acquired during the next year. See this press release for more details and a much larger image, or visit the Messenger website.

Rare elongated crater on Mars

2011-03-05T00:02:00.000-08:00

ESA's Mars Express imaged this elongated crater on Mars. Note that most craters are circular, even when the impactor strikes the planet at a shallow angle. However a train of interplanetary debris can leave an elongated scar, which might account for the crater seen here. But accounting for the origin of that hypothetical debris train can be problematic---perhaps this is debris from a comet or asteroid that was tidally disrupted by Mars? Or perhaps this debris is from a tidally disrupted satellite that had spiraled inwards and onto the planet due to the martian tide. Although this might seem farfetched, this in fact will be the ultimate fact of the Martian satellite Phobos, which will eventually impact Mars in tens of million years, due to its slow orbital decay that is driven by the martian tidal forces. See the Mars Express website for more details.

Monster solar flare imaged by Solar Dynamics Observatory

2011-02-27T18:39:00.001-08:00

This massive solar flare erupted from the Sun's surface on February 24, and was imaged by NASA's Solar Dynamics Observatory. Check the SDO website for more info, plus a very dramatic movie of this explosion in space.

Stardust sees impact site on comet Tempel 1

2011-02-15T18:33:00.000-08:00

The stardust spacecraft flew by comet Tempel 1 last night, and acquired the close-up image of the surface that is seen on the left. Recall that this comet was first visited by the Deep Impact spacecraft in 2005, which shot that comet with a one-ton projectile; the high-res image on the left shows the impact site prior to the collision. One of Deep Impact's science goals was to observe the resulting crater, but the impact generated so much dust, the crater was never seen by Deep Impact. Fortunately, the Stardust spacecraft could maneuvered so that it would encounter comet Tempel 1 six years later. Stardust acquired the fuzzy low-res image on the right, which does indeed show the impact site, with a shallow 100m crater just inside the smaller circle. Note also that the impact obliterated the dark region that is seen at 10 o'clock along the yellow circle (left), in the pre-impact image. The Deep Impact crater has been observed at last!

ISS transits the Sun during solar eclipse

2011-01-04T16:04:00.001-08:00

Thierry Legault captured this amazing picture of the International Space Station as it transits the Sun during a partial solar eclipse by the Moon on January 4.

HR 8799 hosts jumbo planetary system

2010-12-09T18:40:00.001-08:00

Christian Marois (Herzberg Institute of Astrophysics) and colleagues discovered a fourth giant planet orbiting HR 8799. The new planet, 'e' in the above image, lies inwards of planets b,c,d. This is typical when using imaging to hunt for extra-solar planets, since it is the closer-in planets that are harder to find, due to obscuration by the bright central star. A simulated star was actually removed from this image; the fuzzy blob seen in the center is due to imperfections in this star-subtraction process. These planets lie about 15 to 70 AU away from the central star, and have masses of ~5 to 10 Jupiter masses. So this is a jumbo planetary system, since the orbits and masses are several times larger than that the Solar System's. See the abstract of their paper in Nature for more details.

A densely packed planetary system at HD 10180

2010-11-26T15:59:00.000-08:00

C. Lovis and colleagues at the European Southern Observatory in Chile used the 3.6m telescope there to discover 5 or more planets orbiting the star HD 10180. The five certain planets are all Neptune-class, having masses of 12-25 times that of Earth. Also, all orbit rather close to the star, at distances of 0.06-1.4 AU. There is also tentative evidence for an Earth-mass planet orbiting at r=0.02 AU, and a possible 3-Neptune-mass planet orbiting at r=3.4 AU. Ellipses in the above figure show the planets current orbits, while the colored regions indicate their range of motions over time that are due to their mutual gravities. As the figure shows, this system is quite dense with planets, which is actually rather typical for multi-planets extra-solar planetary systems. See the preprint for more details.

EPOXI spots snowballs coming off Hartley 2

2010-11-18T18:42:00.001-08:00

The camera aboard EPOXI also spotted icy chunks jetting off the surface during that spacecraft's close approach to comet Hartley 2. The bigger chunks are golfball to basketball sized, according to this piece in New Scientist.

EPOXI spacecraft flys by comet Hartley 2

2010-11-04T13:01:00.000-07:00

NASA's EPOXI spacecraft flew by comet Hartley 2 this morning. This comet is about 2 kilometers long, with a narrow neck only 0.4 km thick. Note the material jetting off the sunlit end, which is due to the sublimation of surface ice there. Keep an eye on the EPOXI mission page for more images as they get released.

Movies of Saturn's B ring

2010-11-02T08:49:00.000-07:00

The outer edge of Saturn's B ring is controlled by an orbital resonance with the satellite Mimas, whose gravitational perturbations there give the ring-edge a scalloped appearance. That ring-edge has been monitored by the Cassini spacecraft that also orbits there, and several movies showing ring's complex movements are now posted at the CICLOPS website. The above image shows a closeup of the B ring's outer edge seen during equinox, when the sunlight was streaming nearly parallel to the ring place. Note the shadows cast by the bright material at the ring's outer edge. It is thought that these shadows are due to one or more small moonlets also hidden somewhere at the ring-edge. If so, then the moonlet's gravitational pull might be responsible for displacing the ring particles perpendicular to the ring plane, causing particles to pile-up into kilometer-tall mountains that cast those very prominent shadows.

Orcus Patera, a mysterious crater on Mars

2010-08-28T08:31:00.000-07:00

This image of Orcus Patera was acquired by ESA's Mars Express orbiter; see press release. Orcus is an elliptical depression near Mars's equator, near the well-known volcanoes of Elysium Mons and Olympus Mons. Its origin is unknown, possibly a volvanic feature, or perhaps a circular impact crater that was later deformed by tectonic forces.

HD 10180, a five-exoplanet system

2010-08-24T09:38:00.001-07:00

Astronomers used the HARPS radial-velocity instrument (at the European Southern Observatory) to detect five exoplanets orbiting the star HD 10180. Two additional planets are also suspected, but their existence is uncertain due to their weak signal. These five make this exo-planetary system one of the most abundant discovered to date. The five planets are Neptune-class, and they all reside at distances interior to Mar's orbit about the Sun. The above graphic is an artist's rendition of this system. A press release is also available.

Rosetta spacecraft flies by asteroid Lutetia

2010-07-11T12:19:00.001-07:00

The Rosetta spacecraft aquired several images of asteroid Lutetia. Rosetta is headed towards comet Churyumov-Gerasimenko, and will go into orbit about that comet in 2014. But this spacecraft also made a close pass at asteroid Lutetia while en route. Additional images are also posted at the European Space Agency's website. Lutetia might be a C type asteroid, ie a carbonaceous chondrite, which is a fairly common rocky asteroid that is also rich in organic molecules. Or else it is an M type asteroid, which is rich in metallic nickel-iron. M-types must have once resided deep inside the core of a much larger asteroid that likely fragmented early in the Solar System's history. These observations by Rosetta should resolve this asteroid's composition, and may provide clues about its origin.

Daphnis maintains the Keeler Gap

2010-07-09T13:37:00.001-07:00

The small Saturnian satellite Daphnis is responsble for maintaining the narrow Keeler gap, which lies near the outer edge of Saturn's main A ring. Daphnis' gravitational pull on the nearer ring particles also sculpts the gap's edges, resulting in wakes that are downstream of the satellite. This Cassini image is available at the CICLOPS website.

Mass transfer in circumstellar disks

2010-07-07T11:10:00.001-07:00

The left graphic is a near-infrared image of the heirachical star system SR24. The lower object is the star SR24S, and the nebulosity surrounding it is a protoplanetary disk that is composed mostly of hydrogen gas plus some dust. The stellar contribution to this image has been subtracted, which is why the disk appear dark in its center. The upper object SR24N is actually an unresolved binary star; that binary also has its own circumbinary disk such that the SR24N stellar pair + disk orbits the SR24S star + disk. The right graphic is a computer simulation of this system, which reveals that these two disks can transfer mass between each other through a `bridge' that passes through this system's L1 Lagrange point, which is one of three sites in this system where gravity + Coriolis forces balance to zero. Observations such as this will hopefully reveal whether binary stars might one day form planets, or if their disks are too disturbed to produce planets. This image was acquire by Satoshi Mayami at the Subaru Telescope. A preprint on this work is also available.

A big expoplanet in a wide orbit

2010-06-17T12:19:00.001-07:00

The circled dots indicate the 8 Jupiter mass planet that was discovered by David Lafrenière and colleagues as it orbits the star 1RXS J160929.1-210524. A preprint is also available. These infrared images of the system are acquired at wavelengths of 3 (left) and 4 (right) microns. This giant exoplanet orbits about 300 AU away from the primary star (cross), which is quite remarkable, because current models of planet formation generally do not produce such large planets orbiting at such great distances from the star. However, binary stars do exist at these separations, so one might wonder whether these objects really are large exoplanets, or are perhaps rather small stars.

Giant exoplanet confirmed orbiting in debris disk

2010-06-13T11:29:00.000-07:00

Beta Pictoris b is a giant extrasolar planet, having a mass of about 10 Jupiter masses. It was first detected by direct imaging in 2003, but not seen again in followup images acquired in 2008, so the suspicion then was that this faint dot was just a background star, and not a planet that is actually bound to the star. However that expolanet was later recovered again in images acquired in late 2009 by Anne-Marie Lagrange; those images show that the dot seen above is indeed bound to Beta Pictoris, and orbits at a distance of about 10 AU from the star. So it seems that beta Pic b wasn't seen in 2008 because it was passing in front of or behind the very much brighter star.

Beta Pictoris is also known for its huge circumstellar debris disk; that disk is seen edge-on by astronomers at Earth, and the above graphic---which by the way is not a real telescopic image, but is probably the merger of two separate images---shows that the planet's orbit is coplanar with the debris disk. This in fact is to be expected, because such debris disks are composed of dust grains that are produced by collisions among unseen planetesimals, which are also the seeds from which planets form from. See this press release from the European Southern Observatory for more details.

Another impact at Jupiter!

2010-06-04T08:32:00.001-07:00

Anthony Wesley does it again! This time, by recording a video what appears to be another small impact at Jupiter, presumably by an unseen comet or asteroid. Recall that Anthony was also the amateur astronomer who spotted as asteroid impact at Jupiter in July 2009. See New Scientist for a video of the explosion by another amateur astronomer, Christopher Go.

Star formation in the Orion nebula

2010-04-04T18:39:00.000-07:00

This infrared image of the Orion nebula was acquired by the Spitzer Space Telescope in May 2009. The nebula is a gravitating cloud of gas and dust where stars form via collapse of the nebula gas. The bright region at the center is the Trapezium cluster where the hottest and most massive stars have formed. The radiation emitted by these hot stars is also sculpts the cloud by blowing gas and dust out of the cluster. Over time, this loss of gas will over the next few million years ultimately destroy the cluster, because it also reduces the cluster's gravitational binding energy, which then allows the young stars forming within to escape the cluster and join the Milky Way galaxy. Although you can't tell from this particular image, many of the stars forming here also have disks of dust and gas in orbit about them, and these circumstellar disks where planets might also form. See this Spitzer press release for more info.

Outburst by comet Holmes

2010-03-24T11:19:00.000-07:00

Comet 17/P Holmes suffered an outburst in 1892, which led to its discovery then by Edwin Holmes. Causes for a cometary outburst are uncertain, but they might be due to solar heating after close passage around the Sun, or perhaps are due to a collision with another small unseen body. The left image shows comet Holmes' spherical dust coma that was produced after an outburst in October 2007, with the right image showing the comet after its obscuring coma is digitally filtered out. This filtering shows that the coma also hides several cometary fragments that drift away from the main nucleus at speeds of about 100 m/sec. White dots are background stars. These comet fragments also produce dusty streamers as they crumble and fade away, and sixteen such fragments were seen. This image was acquired at the Canada-France-Hawaii Telescope (CFHT) by Rachel Stevenson (UCLA) and colleagues, and a copy of their paper can be found at the arXiv preprint server.

Closeup of Helene

2010-03-10T14:00:00.000-08:00

Cassini acquired this interesting image of the satellite Helene on March 3. Helene is a small 30km-wide satellite of Saturn. Its orbit is also very curious, since it resides at the L4 Lagrange point of the much larger 1000km-wide satellite Dione. The L4 Lagrange point leads Dione's motion by 60 degrees in longitude. Such satellites are known as coorbitals, since they co-orbit with another larger body, and only a few such coorbital satellites are known. This coorbital motion is analgous to the Trojan asteroids, which lead/trail Jupiter by 60 degrees. Note also Helene's smooth surface. Although the outlines of large craters are clearly evident, their filled-in appearance suggests that this satellite is also being bombarded and coated by dust that might also be present in this part of the Saturnian system. Keep an eye on the CICLOPS website for information about this small but interesting satellite.

3D model of Mojave Crater, Mars

2010-02-24T09:56:00.000-08:00

This image is a rendering of a 3D model of the Mojave Crater on Mars. The image was crafted from stereo images acquired by the Mars Reconnaissance Orbiter, and spans about 4km. This is just a small portion of the crater's edge, since the crater itself is 60km across. This image also has its vertial relief enhanced 3x over that in the horizontal direction. Note that this part of the crater appears filled in, like a pond. This ponding is thought to occur when melt generated by an impact is captured behind mountainous walls. The dearth of additional smaller craters tells us this feature is relatively young for Mars, only 10 million years old. Note also the flows into and out of this region. They suggest that the impact event might have melted underground ice that also flooded this region.

WISE view of comet Siding Spring

2010-02-17T16:51:00.000-08:00

NASA's WISE mission (Wide-Field Survey Explorer) is a new spacescraft that is designed to map the sky at infrared wavelengths. The above shows a color image comet Siding Spring seen at 3-22 microns, which is rather redwards of visible light having wavelengths of ~0.6 microns. This image is colored so that the hotter stars appear blue while the much cooler cometary dust tail is red. A tail forms when the comet passes near the Sun, which warms the comet's icy surface. As the comet's icy surface sublimates (boils off), the water vapor also liberates tiny dust grains. Radiation pressure, which is the weak force that sunlight exerts on these tiny dust grains, then sweeps these particles away into a tail that can span millions of miles. See the WISE website for more details.

Closeup of the Deathstar moon

2010-02-15T13:43:00.000-08:00

Cassini's closest ever approach to Saturn's satellite Mimas occurred Saturday Feb. 13. Other pictures of the Deathstar moon are also available at the CICLOPS website.

Hubble image of dust trail in asteroid belt

2010-02-02T07:39:00.001-08:00

David Jewitt (UCLA) acquired this new Hubble image of the mysterious dust trail that appeared recently in the asteroid belt. This trail is also discussed in this January 20 post. Current thinking says that this debris from a recent collision among two asteroids. Check the Hubble page for more details.

Close up view of Prometheus

2010-01-28T15:05:00.000-08:00

On 27 January 2010, the Cassini spacecraft acquired this close-up view of the small 60km Saturnian satellite Prometheus. Shadows cast by its irregular surface suggests that this satellite might have the `flying saucer' shape that is also exhibited by Saturn's other small satellites Pan and Atlas (as detailed in Porco et al 2007). Note that this peculiar shape can result when a satellite forms while orbiting inside a dense planetary ring (such as perhaps Pan, which does orbit in Saturn's main A ring) while also under the influence of Saturn's strong gravitational tide. This in turn suggests that Prometheus (as well as its cohorts Atlas and Pandora) might actually have formed at the outer edge of the A ring and then migrated to its current position just beyond the A ring's outer edge. This kind of radial migration is in fact expected to be driven by the strong gravitational torques that the A ring exerts on the nearby satellites. Check the CICLOPS website for more details.

Recent collision in the asteroid belt?

2010-01-20T15:25:00.000-08:00

This dust trail was imaged by the LINEAR (Lincoln Near Earth Asteroid Research) survey on January 6. The trail is named P/2010 A2, and the arrows point to a faint 200 meter object that is the likely source of this dust. Ordinarily, dusty streaks such as this are comet tails, which form when as the comet's icy surface sublimates (melts). That process also liberates small dust grains from the comet's surface. Pressure due to sunlight then sweeps that dust cloud out into a long tail. Comets are known to inhabit the asteroid belt, but only in the outer part. But this dust trail lies in the inner asteroid belt, where comets are not known to reside. So the current thinking is that this trail, which might only be weeks old, could instead be debris from a recent collision between two asteroids. So this picture could be the first view of the aftermath of a never-before-seen astronomical event---the collision between two asteroids. See this New Scientist article for more details.

Iapetus' dichotomy explained

2009-12-10T17:47:00.000-08:00

Iapetus is Saturn's icy yin-yang satellite. This Cassini image shows that the side of this satellite that leads in its orbit about Saturn is 10 times darker than its polar regions. This darkening was long thought to be due to contamination from Saturn's even more distant satellite Phoebe. Meteorites crashing into Phoebe will launch small debris that goes into orbit about Saturn, resulting in a vast dust ring that also contaminates Iapetus. This dust ring was only recently discovered by the Spitzer Space Telescope. Some of that dark dust gets deposited at Iapetus' leading face, which is then warmed by sunlight. Recent work by John Spencer and Tilmann Denk show that this can cause surface ice there to evaporate at the equator. That water vapor can migrate towards and then freeze out at the poles, brightening the satellite there, and giving it its yin-yang appearance. Additional images can be found at Cassini's CICLOPS website.

Cassini's close look at Enceladus' tiger stripes

2009-11-21T12:53:00.001-08:00

Cassini had a close flyby of Enceladus today. This Saturnian satellite is famous for its tiger stripes, which are warm crevasses in Enceladus' icy surface, seen above. Geysers within those cracks also jet water out into space; these are the faint emissions seen below, which looks obliquely towards the tiger stripes. Additional images from this flyby can be found at the CICLOPS website.

LCROSS: is Moon's water due to comet impacts?

2009-11-20T15:32:00.000-08:00

This image shows the plume that was raised when the LCROSS booster rocket struck the Moon in a region that is permanently shadowed from the Sun. The mission's goal is to search for the water-ice that might be frozen in these shadowed regions, since such ice would be a valued resource for any astronauts that might return to the Moon.

There are two likely sources for this water-ice. One is the solar wind, which can implant hydrogen into the lunar soil, which would then combine with the oxygen in soil to make water. Another source is comet impacts, which can deposit water as well as other volatiles that can then freeze out in these permanently shadowed regions. Since the spectra collected by LCROSS also reveals other volatiles, such as methane, ethanol, ammonia and carbon dioxide, all of which are known to exist in comets, cometary impacts are now a favoured theory for depositing water on the Moon.

Late Heavy Bombardmentmay be due to comet impacts

2009-11-03T06:30:00.000-08:00

The Late Heavy Bombardment (LHB) was a period of intense bombardment of the inner Solar System that is thought to have occurred about 3.85 billion years ago, when the Solar System was only about 700 million years old. Most of the craters on the Moon, including the giant lava-filled basins (also called Mare), are thought to have formed during this brief but intense period of bombardment. Although the Earth would have suffered a similar bombardment, geologic processes have since erased any such craters that formed then.

To study this possible bombardment of the Earth, Jorgenson and colleagues studied ancient sedimentary samples they collected in Greenland that are 3.9 billion years old (see the abstract of his paper). These samples were probably deposited around the time of the LHB. They find that the iridium abundance in those samples are elevated by a factor of 7, which indicates that comets (and not asteroids) are the principal source for the LHB impactors. Evidently, the entire inner Solar System was bombarded by icy comets that likely originated in the outer Solar System. This cometary bombardment might also have been triggered by a sudden rearrangement of the outer planets orbits, Jupiter through Neptune.

Quaoar: a giant rock in the icy Kuiper Belt?

2009-10-13T08:08:00.000-07:00

Wesley Fraser and Mike Brown (Caltech) used the Hubble Space Telescope to place an upper limit on the size of Quaoar, which is a giant Kuiper Belt Object that inhabits the outer part of the Solar System. The Kuiper Belt is the swarm of icy comets that orbit just beyond Neptune, and these bodies represent the debris that was left over when the giant planets formed. The new upper limit on Quaoar's diameter is D<1100km, which Fraser reported at the recent DPS planetary science conference; see his abstract for details. Combining this size limit with Quaoar's known mass (about one-fifth Pluto's) yields a density that is at least 3.5 gm/cm^3. This result is a bit of a surprise, since Quaoar's density is much greater than that of water-ice, while bodies in the outer Solar System are generally expected to be composed mostly of water ice. However, internal heating in a sufficiently large body can temporarily melt it soon after its formation, which would then cause its rocky component to settle to its center before its watery outer layer freezes out. Afterwards, an impact with another large Kuiper Belt may have stripped the young Quaoar of its icy mantle, which would leave its rocky core exposed, and may account for its high density. Although this scenario is rather speculative, it is also quite plausible.

Recent impacts on Mars exposes subsurface ice

2009-09-25T09:38:00.001-07:00

The Mars Reconnaissance Orbiter (MRO) took these images of a 6m crater on Mars in October 2008 (left) and again in January 2009; see this press release for more details. This crater is absent from images acquired in 2007, so it must be due to a relatively recent impact. Note also the bright material in the crater that fades over time. This is to be expected if this were subsurface ice that was suddenly exposed to the surface. Water ice is not stable at the surface of Mars, and will sublimate (vaporize) over time. The MRO spacecraft has discovered several new craters where fresh ice appears to fade over time. This particular crater has a latitude of 43 degrees, which indicates that subsurface ice on Mars extends all the way from from the poles to Mars' mid-latitudes.

Martian gullies at crater's edge

2009-09-05T12:23:00.000-07:00

Gullies are often spotted in sloped terrain on Mars, like the ones seen here at the edge of Hale crater on Mars. This image was acquired by the Mars Reconnaissance Orbiter August 3, 2009; that spacecraft has been observing Mars since March 2006. Martian gullies are of great interest, since their dendritic appearance suggests that groundwater might be seeping out and flowing downhill. However, after many years of study, it is still unclear whether wet or dry processes are responsible for sculpting these gullies. Dry processes include boulders or avalanches that might carve out these gullies as rocks and gravel tumble downhill. Also keep in mind that the martian surface is too cold for liquid water to exist there. Nonetheless, any groundwater would absorb salts from the surrounding rock, which might lower its freezing point enough to exist in liquid form. And where there is liquid water, there is also the possibility for microbial life. For more details, see this press release.

Circumstellar debris disk orbiting HD 32297

2009-08-30T09:22:00.000-07:00

This is the circumstellar debris disk that orbits the star HD 32997, imaged with the Palomar 5m telescope by Dimitri Mawet and colleagues. The star lies at the cross, but its light has been blocked by a phase mask coronograph, which is a device that shifts the phase some of that starlight so that the star's light waves interfere with itself destructively, effectively making the very bright star dissapear from this image. This is very useful, since it also reveals the light from the much fainter circumstellar material.

The colored blobs indicate that there is a ring or perhaps a disk of dust in orbit about this star, with that disk/ring seen nearly edge on. The dust grains are visible because they are reflecting starlight, and the colors indicate the intensity of that reflected light. Of particular interest to me is the asymmetry seen in this disk, with one side being brighter than the other by ~50%.

These dusty disks usually have rather short lifetimes, since dust grains destroy each other when the collide with each other. Consequently, other unseen `planetesimals' are implicated here, since collisions by these asteroidal or cometary bodies are needed to continually resupply the disk with the dust seen here. And since comets or asteroids are evidently forming in this system, it seems plausible that larger planets might have formed here, too. Additional details are also available in the paper by Mawet et al.

Ingredients for prebiotic life found in comet

2009-08-18T12:12:00.000-07:00

The Stardust spacecraft encountered comet Wild 2 on January 2, 2004, and collected samples of the comet's coma and tail. Those samples parachuted to Earth on January 15, 2006, and have been studied in labs ever since. From these samples, Jamie Elsila at NASA/Goddard reports the first ever detection of glycine in a comet. Glycine is a common amino acid, which when combined with others can build proteins, which are important building blocks in the chemistry of life. The detection of glycine in comet Wild 2 strengthens the argument that comet impacts on the early Earth provided the prebiotic chemistry that ultimately allowed life to begin on Earth. However, critics of this cometary-delivery theory would argue that comet impacts are far too fiery and energetic to deposit complex organic molecules on Earth whole and unscathed. Regardless, this interesting finding highlights the value of sample-return missions, which can provide valuable insight into composition of ancient and primitive bodies, like as comets and asteroids, that are the primordial building blocks of the planets. See this press release for more details.

Planetary-sized impacts around HD 172555?

2009-08-11T10:52:00.000-07:00

Casey Lisse (JHU/APL) and colleagues recently used the Spitzer Space Telescope to collect infrared spectra of the dust that orbits the relatively young 12 million year-old star HD 172555. Their observations are described in this preprint. Their spectra shows that this star's circumsteller dust is, as expected, rich in silicate, which is the principle ingredient in circumstellar dust. What is surprising here is that this dust is a glassy silicate, like tektite or obsidian, which tends to form when rocky bodies collide at high speeds of ~10km/sec. These spectra also indicate the presence of ample amounts of SiO gas, which is vaporized rock. From these spectra, Lisse and colleagues infer that this system suffered a recent giant impact via the collision of two large ~1000km bodies (the size of Ceres, the largest asteroid in our Solar System). They estimate that this giant impact occurred within the past ~100 thousand years. There are two possible interpretations of these observations. (1) Collisions among ~1000km-sized protoplanets at HD 172555 indicate that this system is currently undergoing planet formation. This is an important step in the planet-formation process, and is necessary if one wishes to ultimately produce a system of ~10,000km-sized terrestrial planets. (2) Alternatively, giant impacts are instead destroying the protoplanets that orbit HD 172555, and that astronomers are witnessing the collisional destruction of a young planetary system. Which outcome is more likely is presently unclear. See this Spitzer page for more details, as well as the above artist's rendition of a giant impact.

Small moonlet discovered in Saturn's B ring

2009-08-08T08:40:00.000-07:00

The Cassini spacecraft spotted this tiny moonlet as it orbits within Saturn's vast and dense B ring. Again, the rings are observed very near equinox, so the Sun's illumination streams nearly along the ring plane, and small objects can cast long shadows here. From the 40km length of the moonlet's shadow, Cassini scientists can infer its diameter of 0.4km. The view here is of the outer part of the B ring. Saturn is far off to the left, and the dark region on the right is the Cassini Division, in which the Huygen's ringlet (grey ribbon) also resides. Check the CICLOPS website for more details and other great images of Saturn's ring/satellite system.

New radar image of rare triple asteroid system

2009-08-08T08:24:00.001-07:00

A new triple asteroid system was discovered by Marina Brozovic and Lance Benner (JPL) via radar imaging; see this press release for details. Shown here are two small ~50m satellites orbiting a larger 700m asteroid named 1994 CC. Although other triple asteroid systems are known, most are in the main asteroid belt that lies between Mars and Jupiter. However, this is only the second triple asteroid system to have been detected among the near-Earth asteroid population.

Topography at outer edge of Saturn's B ring?

2009-08-06T19:01:00.000-07:00

This very interesting Cassini image shows a close-up of the outer edge of Saturn's B ring. Saturn is far to the left, so the ring's orbital motion here is either up or down (and my best guess says down). The Cassini Division is to the right, just beyond the B ring. The Huygen's ringlet is the prominent gray band that orbits 300km beyond the B ring's edge.

Recall that Saturn is almost at equinox (Tuesday August 11!), so the Sun is just above Saturn's equator. Consequently, sunlight is streaming almost parallel to the ring plane, which allows even very modest vertical structures in the ring to cast long shadows across the ring plane. Evidently, the B ring's outer edge has topography, since it cast shadows that are hundreds of kilometers long! Judging by how ragged the shadows are, this ring-edge seems to resemble a mountain range, which is quite a surprise since the rest of the ring-plane is extremely flat. Note also the bright diagonals, one of which is clearly casting a shadow. These streaks might be due to ring material moving radially, perhaps due to avalanches of ring-matter tumbling down the supposed mountainside? Such radial motion would then get dragged along a diagonal due to the ring's faster orbital speed in regions closer to Saturn. But at this stage, this is all just speculation...

This image was acquired on July 26, 2009, and can be found at the Cassini Equinox Mission's raw image archive. A followup comment will describe how to use this archive effectively to search for other interesting Cassini images.

Vertical ripples in Daphnis' edge-waves

2009-08-01T19:43:00.000-07:00

The small speck casting a shadow here is Daphnis, which is an 8km satellite that orbits within the narrow Keeler gap that lies near the outer edge of Saturn's rings. Saturn is also very near equinox, so the sunlight that is illuminating this scene travels nearly parallel to the ring-plane. Consequently, this small satellite casts a rather prominant shadow across the ring. Daphnis also has a small inclination, so its motion carries it a bit above and then below the ring plane during each orbit of Saturn. Daphnis' gravity then tugs the nearby ring material up and down, too, which results in the vertical ripples that are seen at the Keeler gap's inner and outer edges. Note that these bright ripples also cast shadows as well. This image was acquired by the Cassini spacecraft on June 8, 2009, and many more such images can also be found at the CICLOPS website.

Rover spots meteorite on Mars?

2009-08-01T14:41:00.000-07:00

The Opportunity rover recently spotted this rock on Mars, whose texture resembles a meteorite. The rover is seen using its X-ray spectrometer, which should reveal its composition, and will hopefully determine whether this rock is indeed a meteorite. See this press release for more pictures and details.

New Hubble image of impact site on Jupiter

2009-07-24T13:29:00.000-07:00

This optical HST image of the impact site on Jupiter was collected by Heidi Hammel (SSI) and others using HST's Wide Field Camera 3. This camera is still new and not fully calibrated yet, since it was installed only two months ago by Shuttle astronauts. Nonetheless, it is still able to produce a magnificent image. The current estimate for the impactor diameter is about a third of a kilometer. See this press release for more details.

Great eclipse pictures

2009-07-23T07:51:00.001-07:00

Some wonderful pictures of yesterday's total solar eclipse over Asia are available at planetfunn.blogspot.com.

Keck image shows likely impact on Jupiter

2009-07-20T18:50:00.000-07:00

Above is an infrared image of Jupiter, as observed by Paul Kalas, Michael Fitzgerald and Franck Marchis at the Keck telescope. Note the bright spot, which overlaps the mysterious black spot that recently appeared on Jupiter (see earlier post, below), indicating that this spot is indeed hot. This supports the notion that Jupiter was indeed hit by an impacting comet or asteroid. See New Scientist for more.

New dark spot on Jupiter:due to asteroid or comet impact?

2009-07-20T11:10:00.000-07:00

Anthony Wesley from Murrumbateman Australia reports seeing a black spot in Jupiter's atmosphere. Black spots on Jupiter are reported from time to time, the most famous example of which was due to the impact of comet Shoemaker-Levy 9. That comet orbited Jupiter unseen until 1992, when it was disrupted by that planet's gravitational tide into about 20 fragments during a particularly close approach to the planet. Those fragments then struck Jupiter in 1994, resulting in similarly black (but much larger) bullseyes. Followup observations of this new spot will hopefully reveal whether it might be due to an impact by a comet or asteroid, which is a very rare astronomical event. Stay tuned.

Enceladus might have a saltwater ocean

2009-06-24T19:29:00.000-07:00

Frank Postberg (Max Planck Institute, Germany) has a Nature letter on Cassini's detection of sodium salts in Saturn's E ring; see also this press release. This is a very interesting result, because it implies that Saturn's satellite Enceladus might have a liquid water ocean beneath its icy surface. Recall that in 2005, the Cassini spacecraft spotted geysers shooting tiny ice crystal from cracks in Enceladus' surface (pictured). Those ice grains go into orbit about Saturn and form that planet's tenuous E ring. During subsequent passages through the E ring, Cassini's dust detector was then used to determine the composition of those ice grains, and found them to contain salt at the 1% level. Because those ice grains originated inside Enceladus, Postberg and co-authors argue that these grain's high salinity is possible if, under Enceladus' ice, there is also a liquid ocean there that lies on top of a rocky core that is the source of the salt. Note that there is also an astrobiology angle here, too, since if Enceladus is warm enough to maintain a liquid water ocean, then there is also the possibility for ocean life there, too.

Shadows along the Keeler Gap

2009-06-12T10:09:00.001-07:00

This Cassini image is looking towards the outer edge of Saturn's main A ring. The dark band near the ring's outer edge is the Keeler gap, which is maintained by the small 8km satellite Daphnis, which is the white speck there that casts a shadow across the ring plane. Daphnis' orbit is also inclined slightly relative to the ring plane, which carries it above/below the ring plane with each orbit about Saturn. Due to this up/down motion, Daphnis' gravity on the ring also pulls the nearby ring material at the gap's edge up/down by about 1 km. And because Saturn is near its equinox, the Sun's illumination here is almost horizontal across the ring plane, causing these km-high piles of ring particles to appear brightly lit on their sunward side, which also casts shadows across the ring plane. Check the Cassini/CICLOPS website for more details, or the recent paper in AJ by Weiss et al (subscription required).

Shadows cast by disk-embedded planets

2009-06-10T08:00:00.000-07:00

A recent theory paper by Hannah Jang-Condell (U. Maryland) examines the shadows that might be cast by recently-formed planets as they orbit within the circumstellar disk in which they formed. Her numerical models show that the planet's gravity will 'depress' the disk there. If that disk were then viewed by an astronomer at optical wavelengths, then that depressed spot would resemble a dark pothole, since that depression is not illuminated by the central star (see Figure). The exception is at the pothole's far side, which would instead appear as an illuminated bright spot. Note that extra-solar planets are difficult to see via direct imaging. However this work suggests a new technique that might be used to discover unseen planets indirectly---by searching for these planet's darkened potholes and dimples that they create in a planet-forming disk.

Mars landers:destroying the organics they were sent to find?

2009-05-26T06:58:00.000-07:00

Even if there is no life present on Mars, that planet should have organic molecules on its surface, due to impact delivery by asteroids and comets, which are known to contain organic carbon-bearing molecules. However, organics have not been detected by any landers sent to look for these materials---not by the Viking landers, nor by the more recent Phoenix lander. Organics are detected by heating soil samples in an onboard oven, and looking for their signature in the gases released during heating.

However, Douglas Ming (Johnson Space Center) and colleagues note that the Martian surface contains perchlorate salt, which releases oxygen when heated. Ming's experiments also show that this released oxygen might then burn up any organics present in the soil samples. So if Ming's thinking is correct, this might explain why the Martian landers have not detected organics on Mars---their detection methods might have been burning up the organics that they seek. For more information, see this New Scientist article, as well as Ming's LPSC abstract.

Split Comet Schwassmann-Wachmann 3

2009-05-22T07:20:00.000-07:00

Comet Schwassmann-Wachmann 3 broke up into several fragments in 1995. Its orbit period is 5.4 years, so came closest to the Sun again in 2001 and 2006. Bill Reach and colleagues used the Spitzer Space Telescope to observe this comet in infrared wavelengths in May 2006. The faint band connecting the fragments is a trail of debris that traces their orbit about the Sun. These astronomers detected 55 fragments along this comet's orbit, several of which are seen above. The color image of two brighter components show their dusty tails in red with a hint of green to show that CO2 gas is emitted from the sunward-facing parts of the comet nuclei. These fragments comae and tails are generated as the icy cometary nuclei warm and sublimate (evaporate) in the sunlight, whose weak pressure also sweeps the dust away in the anti-sunward direction. A preprint by Reach et al on these Spitzer observations is also available.

Shuttle transits the Sun

2009-05-15T11:16:00.000-07:00

Space Shuttle Atlantis was photographed in silhouette against the Sun on May 13th by French astrophotographer Thierry Legault, while in Florida. The shuttle's transit across the Sun lasted only 0.8 seconds, and this picture was taken before the shuttle caught up with Hubble. See Legault's website for other other very nice astronomy pictures.

Girl who named Pluto dies at 90

2009-05-13T07:17:00.000-07:00

Venetia Phair , UK, was 11 when Pluto was discovered by Clyde Tombaugh at the Lowell Observatory in 1930. Her grandfather, Falconer Madan, told her of the discovery, and discussed possible names for the new planet. ‘Why not call it Pluto?’, she suggested. Madan passed the suggestion on to friend Herbert Hall Turner, professor of astronomy at Oxford, who in turn telegraphed Lowell Observatory, which endorsed the suggestion. Venetia's grandfather gave her a five-pound note for her idea. Venetia died April 30 in her home in Banstead, England.

Shuttle mission to Hubble

2009-05-11T13:26:00.000-07:00

Space shuttle Atlantis launched today, to service the Hubble Space Telescope for the forth and final time. Astronauts will replace several new cameras and
spectrographs (which will be used to measure the composition of stars, planets, galaxies, etc), and repair others. Astronauts will also replace one of two redundant devices that handle data, will replace Hubble's batteries, and will replace all of the HST's six gyroscopes (which orient the telescope), of which only half now work. One of three Fine Guidance Sensors--which also help point the telescope and are used to hunt for extra-solar planets--will also be replaced. A ring will also be attached to the telescope's backend, so that a rocket can at a later date be attached and used to deorbit Hubble at the end of its life. Hubble has been operating for 18 years, and has been one of the most productive telescopes ever. This servicing mission should extend its life for another 5+ years.

Shadows at the edge of Saturn's B ring

2009-05-07T16:34:00.001-07:00

This fascinating image is from the April 15 Astronomy Picture of the Day. The image was acquired by the Cassini spacecraft, which is in orbit about Saturn. The brighter part of this image is a close-up of the outer edge of Saturn's B ring, while the lower darker part shows the fainter ring material that orbits in the Cassini Division. Saturn is approaching equinox, which means that the Sun is near the ring plane, which also allows the satellite Mimas to cast its shadow on the ring plane (dark vertical streak).

Note also the dark `cookie bites' missing from the outer edge of the B ring. These seem to be shadows cast by something that lies right at the ring edge, possibly very large ring particles orbiting there. But note the bright ringlet that also appears at the B ring's outer edge; if that ringlet is puffy, or otherwise kinky in the vertical direction, then that ringlet might be casting these shadows. Also keep in mind that Mimas has a 2:1 resonance at the B ring's edge, which is where a ring particle orbits twice for every orbit of Mimas. So it is conceivable that resonance might be 'snowplowing' the B ring edge, with ring material also piling up in a vertically above and below the ring-plane as Mimas also shoves it radially inwards. If so, then this snowpiling might instead be responsible for these shadows.

NASA's 2010 budget

2009-05-07T15:54:00.000-07:00

NASA announces its budget for fiscal year 2010. The table is from the budget summary, which shows how NASA spends its money. The 2010 budget is about $18 billion, with more than half spent on Exploration/Space Ops (eg, manned spaceflight), and almost a third on Science, with the rest spent on activities at various NASA centers (Johnson, Ames, etc). Of interest to me is the Planetary Science budget line, which stays flat until year 2011.

Image of planet orbiting Fomalhaut

2009-05-06T05:47:00.000-07:00

This remarkable image shows the motion of the Jupiter-mass planet as it orbits the star Fomalhaut (see inset). This optical image was acquired by Paul Kalas (UC Berkeley) and colleagues using the Hubble Space Telescope. Interestingly, this star also harbors a dusty circumstellar debris disk. The planet orbits just inside a gap within this disk, and its gravity is responsible for keeping that gap clear of dust. Note also that the debris disk appears to resemble a ring, due to the disk's inner edge being illuminated by the central star. The dust in these debris disks is thought to be generated by collisions among unseen planetesimals (eg, asteroids or comets) that also probably orbit within this disk. The ellipse in this graphic has a radius of 30 AU (1 AU = Sun-Earth distance), which is the radius of Neptune's orbit. The radius of the disk's inner edge is about 140 AU, which is about 3 times larger than the size of our Solar System's Kuiper Belt, which is also a belt of comets orbiting just beyond Neptune.

Welcome to Solar System Watch!

2009-05-06T04:10:00.000-07:00

First post...welcome! This blog is devoted to the latest astronomy news, with a special emphasis on planetary science, which is also my field of study. And if you are wondering who is doing the blogging here, please have a look at my profile.

The blog's title graphic is extracted from this image of Saturn that was acquired by the Cassini spacecraft on May 4 , 2005. Here we are looking obliquely onto the dark side of the ring plane. Saturn was in winter when this image was acquired, so the Sun is south of the rings, which also cast shadows onto Saturn's northern hemisphere.