96% Chance of Nothing Happening on Mars

Or, put another way, the chances of impact on Mars are 1 in 25.

Bad Astronomy and the Planetary Society Blog have more information.

Asteroid May Hit Mars!

NASA just put out a press release announcing the possibility that an asteroid 164 feet (50 meters) across may slam into Mars next month. Based on the uncertainties in its trajectory, scientists are giving it a 1 in 75 chance of impact. The asteroid is traveling at about 30,000 miles per hour. If it hits Mars, the impact would release as much energy as three million tons of dynamite, and would leave a crater more than a half-mile wide.



It will be really interesting if this thing actually does impact Mars. There are enough spacecraft on and around the red planet that we would get some really interesting information about the effects of medium-sized impacts (not to mention some awesome pictures of the aftermath). A lot of the press releases have been comparing this potential impact with the Tunguska event: a large explosion over Siberia in 1908. This is misleading though, because the Tunguska event was likely caused by a mid-air explosion of an asteroid, rather than an impact into the surface. Since the explosion happened in mid-air, nobody is quite sure how large the impactor was. In fact, recent results show that it may have been only 20 meters across!

In any case, I find it pretty amazing that we are good enough at tracking rocks in space to be able to tell whether or not they will hit, not just the earth, but any other planet as well. This potential impact on Mars should also serve as a reminder that things like this can and do happen to earth too.

The Arecibo radar/radio telescope has been crucial in identifying and studying near-earth asteroids, but recently its funding for planetary radar was cut to save a few million dollars. Planetary radar is the best way to track potentially dangerous objects, and Arecibo is 20 times more sensitive than any other radar telescope. Arecibo's planetary radar could literally save the world, and it is being shut down to save money. To learn more, check out this statement from the Planetary Society.

Astronomy Pictures of the Year

The Astronomy Picture of the Day website just put up their choices for Astronomy Picture of the Year 2007. Believe it or not, my personal favorite is not a photo of Mars. It's of the spectacular Comet McNaught from last January:

Hot Jupiters

(Image Credit: NASA)

Picture a world where the year is 5 earth-days long, and the sun never rises or sets, but remains fixed directly overhead. The cloud tops on the sunlit side of the planet are thousands of degrees, and are made of vaporized minerals and metals. Iron smog and wisps of quartz are shunted from the scorching daylit side to the perpetually dark night side, which glows a dull red, pouring its excess heat into space. The upper hydrogen atmosphere is continually ripped from the planet and streams out into space like the tail of a comet.

Although it sounds like it belongs in the realm of science fiction, this description may actually be quite accurate for many of the planets that astronomers have found around other stars. The most successful method for detecting planets, called the "radial velocity" method, relies on detecting the small motions of stars as their planets orbit and tug them back and forth. Just as the siren on an ambulance is higher pitched when it is approaching than when it is receding, the light from a star looks slightly bluer when the star is moving toward us and slightly redder when it is moving away. Since the size of the shift depends upon the mass of the planet and how rapidly it orbits, many of the exoplanets discovered are larger than Jupiter, and orbit their star in a matter of days.

The first "hot jupiters" were a shock to the scientific community because it is thought that gas giants have to form very rapidly, before their star becomes hot enough to blow all of the primordial gas out of the system. To form so rapidly, most formation theories require the giant planets to form far enough out in the solar system for ices to be present. Too close to the sun and the only things that can clump together to form the seed for a giant planet are rocks. Farther out, beyond the so-called "snow line", ice can also clump together with the rocks, allowing the cores of giant planets to form rapidly and accumulate gas before it gets blown away.

Because ice appears to be required to form giant planets, how can they possibly form so close to their stars? The answer is: they don't! The latest research suggests that in the early days of a solar system, the planets move around quite a bit. Often, big planets toss small things like comets, asteroids, and protoplanets out of the solar system. As they fly off into interstellar space, these small pieces of debris take energy and angular momentum from the giant planet with them. The result is that giant planets tend to drift inward as they fling things outward. At the same time, if there is still gas in the system, the planet will also interact with that gas, creating waves. These waves also steal the planet's angular momentum and send it spiraling inward. In this way, a giant planet could conceivably form in the icy outer reaches of the solar system and then bully its way inward, scattering debris and making waves as it does so.

The story of hot Jupiters is a great example of science in action: giant planets were discovered a lot closer to their stars than they had any right to be, based on our understanding of planet formation. Far from weakening the theory however, the discovery of "hot jupiters" let scientists to figure out that planet migration is a very important process in the formation of a solar system. The theory emerged stronger than ever, able to explain a wider variety of potential solar systems.

So, next time you step outside, take a look at the rocks on the ground and think about a world so hot that those rocks vaporize and form clouds. And then, while you're marveling at that idea, remember that worlds like that really do exist!

"The Universe is not only queerer than we suppose, but queerer than we can suppose." - J.B.S. Haldane


Image credit: European Space Agency, Alfred Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS, France) and NASA.

Science Debate!

There has been a recent movement among science blogs and activists to organize a science debate for the presidential candidates. This is, in my opinion, an excellent idea. It would not have to be like a science test, nobody expects candidates to be scientists, but we should expect them to be in touch with reality, and to understand how science affects policy. As our society becomes more reliant upon technology and faces challenges in medicine, energy, defense, and the environment, a scientifically literate president is crucial. I encourage everyone to check out the official Science Debate 2008 website, and read some of the excellent blog posts, and editorials on the topic.

Spirit Rover has Camoflage!?

In this recent "deck pan" of the Spirit rover, the solar panels are so covered in dust that they blend in almost perfectly with the surrounding dusty martian surface.





All that dust means that the rover has less power to work with every day. With martian winter approaching in a few weeks, the Rover team has been working nonstop trying to drive Spirit to a location where the solar panels will be tilted toward the sun. The rover will camp there, trying to conserve energy until spring comes and there is enough power to drive once again.

Here's hoping for a gust of wind to clean off the panels and make life a little easier for Spirit...

A Candle in the Dark

Once finals are over, I will make a few honest-to-goodness posts, where I actually write a lot about something interesting. For now, enjoy this cartoon I found, and the Sagan quote that expresses the same idea but with a somewhat different tone...




"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive. Where have we heard it before? Whenever our ethnic or national prejudices are aroused, in times of scarcity, during challenges to national self-esteem or nerve, when we agonize about our diminished cosmic place and purpose, or when fanaticism is bubbling up around us-then, habits of thought familiar from ages past reach for the controls.

The candle flame gutters. Its little pool of light trembles. Darkness gathers. The demons begin to stir."
- Carl Sagan, The Demon-Haunted World: Science As a Candle in the Dark