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.

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.

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.

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.

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.

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.

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.