# Asteroid may strike Mars

1. Dec 23, 2007

### tony873004

The asteroid 2007 WD5 was reported as having a 1 in 75 chance of hitting Mars on January 30, 2008. This was based on observations through December 21, 2007. New observations are in.

It's predicted path is getting closer to Mars. The media won't run another story until NASA makes another press release, but the updated numbers from some additional observations are now available. December 23rd's data shows it is now predicted to pass 17631 km above the Martian surface, more than twice as close as the prediction made with December 21st's data, when the odds of collision were placed at 1 in 75.

This doesn't necessarily mean that the odds of 1 in 75 have improved. I don't know what the error bar is on the new data. Perhaps as well as the asteroid's trajectory moving closer to Mars, the error bar has shrunk enough to confidently exclude a Martian collision. Or perhaps not.

Here's a screenshot from Gravity Simulator showing the asteroid's trajectory:

2. Dec 24, 2007

### Gokul43201

Staff Emeritus
3. Dec 24, 2007

### tony873004

The latest data is not from a press release by NASA. It is from propogating the data obtained from a direct query of JPL / NASA ' s Horizons Ephemeris Computation Service

Code (Text):
Rec #:621446 (+COV) Soln.date: 2007-Dec-23_00:50:04 # obs: 28 (41 days)
This is the most current data available, but it will likely change from day to day.

In your first link, it's strange how they say "may pass within 30,000 miles of Mars at about 6 a.m. EST (3 a.m. PST) on Jan. 30, 2008". Yet the data available on the 21st had the asteroid passing just under 50,000 km from Mars' surface at 9:11 GMT, which is 1:11 Pacific Time, not 3am PST as the article states.

4. Dec 24, 2007

### pixel01

What surprised me (and scared) is that the asteroid was not discovered until it approached quite near the Earth, and just recently: Nov.20 !

5. Dec 27, 2007

### B. Elliott

If it has a 1 in 75 chance of actually impacting Mars, what would the odds be of it at least getting captured by the planet? Has to be better than 1 in 75.

Could we watch WD5 become a temporary Mars satellite? Or are the conditions "not so right" for this to happen?

6. Dec 27, 2007

### D H

Staff Emeritus
The odds of being captured are practically the same as the odds of collision. The asteroid is in a hyperbolic orbit. A slew of coincidences need to occur for something to be captured.

Think of it this way: Mars is a lot closer to the asteroid belt than is the Earth. As such, it has a lot more "close calls" than does the Earth. The number of asteroid fly-bys of Mars vastly overwhelms the number of captures. Mars has but two satellites after all.

7. Dec 27, 2007

### ranger

I'm sort of hoping there will be an impact. At least this will expose some subsurface for remote observation.

8. Dec 27, 2007

### B. Elliott

Does it primarily have to do with how quickly gravity's influence drops off with distance? I remember hearing somewhere that if you move twice the distance away, the pull drops by 1/4. Are there any graphical charts you know of that show this?

9. Dec 27, 2007

### D H

Staff Emeritus
Newton's law of gravity, $F=Gm_1m_2/r^2$. If it were only the asteroid versus Mars, and Mars had no atmosphere, Mars would never capture the asteroid. Its simple orbital mechanics.

To be captured, the asteroid would have to have an orbit much closer to Mar's orbit than it does (its orbit about the Sun relative to Mars' orbit about the Sun gives it too much energy), it would have a closest approach more-or-less above the sunrise line (it will get a huge velocity boost if its closest approach is on the sunset side, kind of like dropping a ping pong ball on top of a superball gives the ping ball a HUGE bounce), and it would have to hit Mar's atmosphere hard enough to slow it down considerably but not so hard to make it burn up.

10. Dec 27, 2007

### rbj

well, if Mars (and the asteroid) were a point mass (which they ain't). think of the surface of the planet as the extent of the atmosphere. a very dense atmosphere.

11. Dec 28, 2007

### rbj

and, it might be a useful canary for the politicians to take more seriously the near Earth bodies that may someday trouble our planet. wouldn't that be an Armageddon if a yucatan-sized thing visited our planet again?

12. Dec 28, 2007

### D H

Staff Emeritus
Capture, in the context of this discussion, excludes collision with Mars' surface. In other words, Mars gets a new satellite. I suppose that Mars' non-spherical nature could contribute to capturing an asteroid on a hyperbolic trajectory. However, that strikes me as far, far flukier than Mars capturing an asteroid that just misses Mars and performs an aerobreaking maneuver instead.

13. Dec 28, 2007

### tony873004

This asteroid is moving very fast with respect to Mars. There is no chance of capture. Even if it were moving slowly with respect to Mars, the best it could hope for is capture into a temporary orbit. Earth recently had a 2nd moon. It orbited a few times and then escaped.

14. Dec 28, 2007

### D H

Staff Emeritus
I agree. I did not word post #6 very well. I should have said "The odds of being captured or colliding are the same as the odds of collision. (In other words, there is no chance of capture)."

15. Dec 29, 2007

### neutrino

News Update: Chances are now http://www.skyandtelescope.com/r?19=961&43=107891&44=12905456&32=3186&7=162451&40=http%3A%2F%2Fwww.skyandtelescope.com%2Fnews%2F12905456.html [Broken].

Last edited by a moderator: May 3, 2017
16. Dec 29, 2007

### hypatia

I wonder if Los Vegas has started betting on it yet?

17. Jan 3, 2008

### OmCheeto

now 1 in 28

http://neo.jpl.nasa.gov/news/news154.html [Broken]

still no news from las vegas.

Last edited by a moderator: May 3, 2017
18. Jan 3, 2008

### neutrino

Drat!

19. Jan 4, 2008

### pixel01

Well, they can not see the asteroid since so it's not surprising if tomorrow you will hear the oods should be 1/24 or something.

20. Jan 11, 2008

### Gokul43201

Staff Emeritus