Thursday, December 9, 2010

HR 8799 hosts jumbo planetary system

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.

Friday, November 26, 2010

A densely packed planetary system at HD 10180

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.

Thursday, November 18, 2010

EPOXI spots snowballs coming off Hartley 2

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.

Thursday, November 4, 2010

EPOXI spacecraft flys by comet Hartley 2

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.

Tuesday, November 2, 2010

Movies of Saturn's B ring

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.

Saturday, August 28, 2010

Orcus Patera, a mysterious crater on Mars

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.

Tuesday, August 24, 2010

HD 10180, a five-exoplanet system

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.

Sunday, July 11, 2010

Rosetta spacecraft flies by asteroid Lutetia

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.

Friday, July 9, 2010

Daphnis maintains the Keeler Gap

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.

Wednesday, July 7, 2010

Mass transfer in circumstellar disks

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.

Thursday, June 17, 2010

A big expoplanet in a wide orbit

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.

Sunday, June 13, 2010

Giant exoplanet confirmed orbiting in debris disk

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.

Friday, June 4, 2010

Another impact at Jupiter!

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.

Sunday, April 4, 2010

Star formation in the Orion nebula

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.

Wednesday, March 24, 2010

Outburst by comet Holmes

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.

Wednesday, March 10, 2010

Closeup of Helene

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.

Wednesday, February 24, 2010

3D model of Mojave Crater, Mars

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.

Wednesday, February 17, 2010

WISE view of comet Siding Spring

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.

Monday, February 15, 2010

Closeup of the Deathstar moon

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.

Tuesday, February 2, 2010

Hubble image of dust trail in asteroid belt

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.

Thursday, January 28, 2010

Close up view of Prometheus

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.

Wednesday, January 20, 2010

Recent collision in the asteroid belt?

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.