Space Fan News 59: Ice on Mercury?; Runaway Planets Are Fast; Transporting Life


Uploaded by tdarnell on 23.03.2012

Transcript:
Hello Space Fans and welcome to another edition of Space Fan News.
Remember a little over a year ago, the MESSENGER spacecraft went into orbit around Mercury?
Well this past St. Patrick's Day, March 17th marked the end of its one year primary mission
and we have learned more about Mercury in that one year than we have in all the years
since it was first discovered combined.
Up until now, it has been the least studied planet in our solar system, but all that has
changed.
The data from MESSENGER paint a very strange picture of Mercury. Over the course of the
last year, it has taken nearly 100,000 images and has returned data that have taught us
lots of new things about the planet, including what its surface looks like, the structure
of its core, and we've looked into areas in permanent shadow at the poles that contain
some mysterious, highly reflective polar deposits.
Using the laser altimeter onboard, we now have a precise topographic model of the planet's
northern hemisphere. From this, we see that Mercury doesn't have as wide a spread of elevations,
from the lowest points to the highest, as the Moon has. The most prominent feature is
an extensive area of lowlands in the high northern latitudes that is home to the volcanic
northern plains.
The other thing we've learned from MESSENGER is something I think is really cool. Literally.
One of the primary goals for MESSENGER was to look at bright spots at the poles of Mercury
that were seen in radar observations taken from Earth.
The leading theory was that these bright spots were frozen water ice deposits.
Ice on Mercury, how can that be?
Well, there are areas near Mercury's south pole that are in permanent shadow and near
the north pole they also saw these bright spots in shadowed regions.
Parts of Mercury exposed to the Sun can get as hot as 427 Celsius, while the shadows can
get down to minus 184 Celsius.
For Americans, that's 800 degrees to minus 300 degrees F.
So when MESSENGER looked at these spots with cameras, the images seemed to support the
theory that it's water ice, but it isn't conclusive. For one thing, for those bright spots to be
water ice, there would have to be a thin layer of insulation to keep it colder than the surface,
which can get above freezing, and they haven't seen evidence of that yet.
Next, did you know that some of the fastest objects whirling around in galaxies may be
runaway planets?
Researchers from the Harvard Center for Astrophysics have found that runaway planets may approach
speeds up to a few percent the speed of light. This would make them some of the fastest objects
in a galaxy.
So what's a runaway planet?
Well, to understand that, we need to set the wayback machine to seven years ago when astronomers
were surprised by the discovery of the first-ever star seen flying out of out galaxy at one
and a half million miles per hour.
After scratching their heads and doing what astronomers do best, looking up, they found
that these fast moving stars, called hypervelocity stars, are created when a double-star system
wanders too close to the supermassive black hole at the galactic center.
The strong gravitational forces rip the stars from each other, sending one away at high
speed while the other is captured into orbit around the black hole.
Well, this was so interesting that astronomers started to wonder if the same thing could
happen to planets. They found that not only do hypervelocity planets exist, but they can
go much faster than stars.
A typical hypervelocity planet would slingshot outward at 7 to 10 million miles per hour.
However, a small fraction of these could gain much higher speeds under ideal conditions.
We can't see these planets with our current telescopes in space or on the ground, they
are too dim, distant and this doesn't happen all that often.
But… you know what I'm gonna say, don't you?
Yes, that's right. Hubble may not be able to see 'em, but JWST can.
As we used to say in the Army, "That's what I'm talkin' about."
Finally, scientists from Purdue looked at the planets around Gleise 581 to study how
easy it would be for material - some of which might contain living microbes - to go from
one planet to another. They were particularly interested in transferring material from a
super-Earth, since we've found so many of those things in our search for exoplanets.
Planets within a solar system exchange material all the time. We've found rocks from Mars
and the Moon here on Earth. In fact, it's entirely possible that life started on Mars
and then came to Earth, hitchhiking on some of these rocks.
So it's a very interesting thing to find out how often this happens. There is even a lot
of discussion about the possible spread of life from one star to another.
These guys from Purdue studied Gliese 581 because Planet d, which is a super-Earth,
falls in a habitable zone where liquid water might exist.
What they found by studying Gliese 581 is that it's very difficult for stuff to spread
throughout that system in the same way that it could in our solar system.
All four planets found in Gliese 581 are within close proximity to their central star, which
means they have large orbital velocities. These things are really flying around their
stars. But, it turns out that the initial velocity of material leaving Planet d is not
enough to allow exchanges among planets.
This means that Planet d doesn't have a very good chance of transferring material to the
other planets in the that system and, because of that, it is far more isolated, biologically,
than Mercury, Venus, Earth and Mars are.
I think this study really shows us how unique our solar system is.
I think the takeaway from this is that since Gliese 581 is pretty typical of the exoplanet
systems discovered so far, what happens there is a good indicator of what all the other
planets we've found so far may be like.
If that's true, then none of the solar systems that we've found so far would be able to exchange
material that could transport life among the different planets there anywhere near like
what our own solar system offers.
Which means that one of the most important mechanisms for propagating life throughout
the universe, may not be very common.
Bummer.
Well, that's it for this week Space Fans, thank you for watching and, as always, Keep
Looking Up!