A good chunk of the exoplanets that we’ve detected so far are huge, Jupiter-sized and larger. A lot of them are orbiting their stars at very short distances – it might seem strange to think that planets bigger than Jupiter are orbiting their stars closer than Mercury orbits the Sun, to the point where some of them take days or only fractions of a twenty-four hour day to complete one full orbit, but that’s what we’ve actually observed (among other really cool kinds of exoplanets). For comparison, Jupiter takes about twelve Earth years to travel around the Sun once, and these giant Jupiter exoplanets orbit in only fractions of that time. Exoplanets like these are called hot Jupiters, so named of course because while they’re “jovian” (Jupiter-like) in size, their proximity to their parent stars means that their surface temperatures are several hundred times as high as those of our outer planets. Hot Jupiters don’t start out at their sweltering homes though, and how they get there is pretty interesting.
In protoplanetary and debris disks (the millions of miles of stuff around a young star, yet to conglomerate into bigger objects like planets and asteroids), material is concentrated in rings. To maintain that ring structure (rather than have the material swirl out into thinner and thinner strands until an even distribution of matter is achieved), the rings can’t be shaped in perfectly concentric circles. Rather, each ring is tilted just a little to one side with respect to the one inside it, creating a twisting effect that causes some sections along each ring to be bunched up closer together, and some sections to be spaced out farther apart. This causes the matter in these bunched-up areas to be packed more densely than the places spread farther out. Just like how it’s easier to fit ten people into a van than it is into a sportscar, the amount of stuff there is doesn’t change – just how it’s being packaged. It helps to take a look at the diagram to picture this, since there you can really see how the subtle tilts in each ring contribute to the swirling effect.
A diagram of the structure of spiral density waves, credit Dbenbenn and Mysid; distributed via Creative Commons License
This, incidentally, is also what gives spiral galaxies their shape – on a much bigger scale, of course! Read more »
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Hubble captured this wonderful image that looks very much like an outer space firework explosion. Herbig-Haro 110 is a geyser of hot gas being blown away from a newborn star that ricochets off the dense core of a cloud of molecular hydrogen. Herbig-Haro 110 is one of a collection of the group of Herbig-Haro objects that come in a variety of shapes, but still have the same basic configuration. Twin jets of heated gas are ejected out from a newly formed star and stream through the space between stars. Astronomers suspect that these jets are fueled by gas and dust falling onto a young star. The disk acts as the fuel tank, the star acts as the gravitational engine, and the jets are the exhaust. When these jets slam into the gas between stars, it heats up the gas, causing it to glow. Gas within the shock front slows dramatically, but more gas just keeps building up behind it, causing more glowing (These “bow shocks” are so names because they resemble the waves that form at the bow of a boat). By studying these structures carefully, astronomers can “rewind” them, in a way, in order to study the star’s history. Read more »
We have had three rare celestial events in succession – an annular
solar eclipse on May 20 (May 21 in the Eastern Hemisphere), a partial
lunar eclipse on June 4, and a Transit of Venus on June 5/6.
Credit: Shannon Hall
Credit: Craig Markwardt
The first image here is a composite image of several stages of the annular solar eclipse taken from New Mexico. The second is a lucky shot of the Venus transit caught in a thin strip between clouds.
Of these, the Transit of Venus is not visually spectacular – when Venus moves in front of the disk of the Sun as seen from the Earth, it only casts a small shadow, and the shadow is not all that impressive even in images taken with a properly equipped camera (staring directly at the Sun can be damaging to your eyes and to your cameras!) However, the transit probably was the most important event of the three, historically speaking. This is because the observations of transits of Venus are very rare and in the past they were used to establish the scale of the solar system. Read more »
There are gorgeous new images out from NASA’s Cassini spacecraft. Here, Saturn’s third-largest moon, Dione, can be seen through the haze of the planet’s largest moon, Titan, in this view of the two posing before the planet and its rings. There are more on the Cassini website.
NASA’s Mars Reconnaissance Orbiter has revealed new images that show some Martian slopes that change over the course of the Martian seasons. The scientists involved in the project think that best explanation for these seasonal changes would be the flow of salty water, much like our oceans. I wonder what the Martian beach crowd is like…
Mars Reconnaissance Orbiter images show dark deposits on a crater wall that may be from seasonal water flow on Mars.
Image credit: NASA/JPL-Caltech/Univ. of Arizona
The James Webb Space Telescope has had a lot of recent milestones. All the primary mirror segments have been polished – and the secondary mirror has just been completed. You can read a NASA web feature all about what Webb’s secondary mirror does and why it’s important. (It’s quite large too – nearly as big as the Spitzer Space Telescope’s primary mirror!)
This stunning new image was taken of the first six James Webb Space Telescope flight mirrors were being prepped for cryo testing at Marshall Space Flight Center. You can read more about this mirror milestone in the NASA.com feature.
We’ll soon have some excitement when the ISIM (the structure that will hold the James Webb Space Telescope’s instruments) gets put on the giant centrifuge here at NASA Goddard! Read the release to find out more about why they going to spin the ISIM on a centrifuge!
Credit: NASA/Chris Gunn
Here’s what the centrifuge looks like spinning. Geeked on Goddard has a whole feature written about it and this exclusive footage:
The makings of new planets lie in dusty, debris-filled disks rotating around stars, held in place and shaped by the influence of their host stars. But the dust, ice, and small bodies in these planet-forming disks also feel the effects of a system’s motion through space – and interaction with interstellar gas can warp a dusty disk into a weird and unexpected shape.
We spoke with Goddard astrophysicist John Debes about his team’s research into these oddly-shaped disks. Using the Hubble Space Telescope, scientists are investigating these disks in hopes of finding clues about how other planetary systems are formed – and perhaps even discovering the origins of our own.
RT @thinkgeek: We donated to Astronomers Without Borders today 'cause spaaace! Pics from @NASAGoddard tour & how Timmy got to space: http:/…about 6 hours ago
Blogs | Jillian Brown | 
August 3, 2012 6:41 pm | 
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