
Thursday, December 10, 2009
Iapetus' dichotomy explained

Saturday, November 21, 2009
Cassini's close look at Enceladus' tiger stripes


Friday, November 20, 2009
LCROSS: is Moon's water due to comet impacts?

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.
Tuesday, November 3, 2009
Late Heavy Bombardment
may be due to comet impacts

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.
Tuesday, October 13, 2009
Quaoar: a giant rock in the icy Kuiper Belt?

Friday, September 25, 2009
Recent impacts on Mars exposes subsurface ice

Saturday, September 5, 2009
Martian gullies at crater's edge

Labels:
astrobiology,
life,
Mars,
Mars Reconnaissance Orbiter
Sunday, August 30, 2009
Circumstellar debris disk orbiting HD 32297

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.
Tuesday, August 18, 2009
Ingredients for prebiotic life found in comet

Tuesday, August 11, 2009
Planetary-sized impacts around HD 172555?

Labels:
asteroids,
dust,
planet formation,
protoplanets,
silicate
Saturday, August 8, 2009
Small moonlet discovered in Saturn's B ring

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

Thursday, August 6, 2009
Topography at outer edge of Saturn's B ring?

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.
Saturday, August 1, 2009
Vertical ripples in Daphnis' edge-waves

Rover spots meteorite on Mars?

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.
Friday, July 24, 2009
New Hubble image of impact site on Jupiter

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.
Thursday, July 23, 2009
Great eclipse pictures

Monday, July 20, 2009
Keck image shows likely impact on Jupiter

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

Wednesday, June 24, 2009
Enceladus might have a saltwater ocean

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.
Friday, June 12, 2009
Shadows along the Keeler Gap

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).
Wednesday, June 10, 2009
Shadows cast by disk-embedded planets

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.
Tuesday, May 26, 2009
Mars landers:
destroying the organics they were sent to find?
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.
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.
Friday, May 22, 2009
Split Comet Schwassmann-Wachmann 3


Friday, May 15, 2009
Shuttle transits the Sun

Wednesday, May 13, 2009
Girl who named Pluto dies at 90

Monday, May 11, 2009
Shuttle mission to Hubble

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.
Thursday, May 7, 2009
Shadows at the edge of Saturn's B ring

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

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.
Wednesday, May 6, 2009
Image of planet orbiting Fomalhaut

Welcome to Solar System Watch!

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.
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