2009 HC82 ~ 2km - 3km asteroid that orbits the Sun backwards

[Smersh]

I reckon MeteorWayne must have heard of this one by now ...

Story from New Scientist:

The discovery of a 2- to 3-kilometre-wide asteroid in an orbit that goes backwards has set astronomers scratching their heads. It comes closer to Earth than any other object in a 'retrograde' orbit, and astronomers think they should have spotted it before.

The object, called 2009 HC82, was discovered by the Catalina Sky Survey in Arizona on the morning of 29 April.

From observations of its position by five different groups, Sonia Keys of the International Astronomical Union's Minor Planet Center calculated it orbits the sun every 3.39 years on a path that ventures within 3.5 million km of the Earth's orbit. Combined with its size, that makes 2009 HC82 a potentially hazardous asteroid.

What's really unusual is that the calculated orbit is inclined 155° to the plane of the Earth's orbit. That means that as it orbits the Sun, it actually travels backwards compared to the planets. It is only the 20th asteroid known in a retrograde orbit, a very rare group. None of the others comes as close to the Earth ...

Full story here.

Here's the interactive orbit diagram along with the orbital elements and parameters. (You'll need Java enabled to see and use the orbit diagram.)

Next closest approach to Earth seems to be 0.158 AU on Jan 4th 2012. On Feb 10th 2012 it seems to come very close to Mercury (but diagram does not give the distance.) It's possibly even closer to Venus on April 4th, 2015.

I wonder why it's in such an unusual orbit? (And as far as Earth is concerned, I hope the orbit is correctly calculated and it doesn't approach any closer.)

PS - if this would be better in ATA please feel free to move it it, cheers.

 

[MeteorWayne]

Hi Smersh, thanx. Actually, I've been busy for the last day or two.

IIRC, there was one within the last month that was in my "Close approaches to earth" thread (which is here in SS&A, I figure this is the best forum unless it will be observable, when I might want it in AtA).

IIRC, it came closer to earth, so I think the article is incorrect, but I'll check.

Edit: I still think I saw a recent one, but it is not mentioned in any of the threads here in SS&A. I'll rack my brain to see if I can figure out what I think I remember.

I'm also skeptical of the claim there are only 20 retrograde asteroids, but that will be harder to check out; not sure how to even do that. Since there are more than half a million known, that percentage seems very low.

Note it does not show up on JPL's Sentry Impact Risk page, so at least for the next century, it is not a threat to earth.

Most likely it was moved to that kind of an orbit after interaction with Jupiter some time in the distant past.

Edit: After examining the orbit, it seems quite likely that this asteroid might be a degassed comet nucleus. About 3% of named periodic comets are retrograde. I've discussed that in some detail in another thread, which may or may not still exist.

MW

 

[R1]

What would happen to a tether or a flexible solar sail if they were placed in the path of of the bolide ?
Would it evaporate on impact, or possibly survive?

another question,
if it collides with the moon, would it be the end of humanity ?

 

[MeteorWayne]

A few items:

First, this object has been added to the JPL Sentry Impact Risk Page....that's not a good thing.
Most of that is an artifact of the very short observational arc (only 4 days) so the potential errors in the orbit are quite large, as well as the huge potential impact velocity due to it's retrograde orbit. Were this object to hit the earth, the impact speed would be about 61 km/sec (That's 38 miles per second or ~ 136500 mph). Compare that with a typical asteroid impact velocity around 40,000 mph. There are currently 31 vitual impactors (VI) beginning Jan 13, 2012 (insert scary theremin music here). The estimated size has been reduced a bit, with 1.9 km at the center of the range.

Still at that speed, since KE= 1/2 times (velocity squared) the impact energy would be 4.3 million Megatons. That'll leave a mark.

As is usual, as more observations come in, the impact risk will likely be reduced, and hopefully disappear.

Regarding any object like a solar sail in it's path, at that speed, unless it is traveling in a retrograde orbit at 30 km/sec, it would be vaporized.

If it hit the moon, it probably wouldn't be fatal to the erath, but it sure would shake things up.

As of the current time, it is now the most dangerous asteroid listed on the Sentry page, although the impact probabily is VERY low due to the orbital uncertainties. This is counterbalanced by it's large size and exceptionally high impact velocity.

As I said, I suspect it is actually a degassed comet nucleus, as it is in a typical Jupiter family comet orbit, with a certain technical parameter (called the Tisserand parameter) suggesting it may have been a Halley family comet that was just captured into this shorter period orbit. (~ 3.75 years period)

Here is the Solar System database page for this object as listed above:

http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2 ... ;cad=0#orb

Here is the Sentry Impact Risk Summary page for this object:

http://neo.jpl.nasa.gov/risk/2009hc82.html

Here is the Sentry Impact Risk Page for all objects:

http://neo.jpl.nasa.gov/risk/

Here is the new NEODys Home Page:

http://newton.dm.unipi.it/neodys/

The new NEODyS Risk page:

http://newton.dm.unipi.it/neodys/index.php?pc=4.1


And the NEODyS page for this object:

http://newton.dm.unipi.it/neodys/index. ... n=2009HC82

More later...

MW

 

[R1]

from the OP article:

astronomers think they should have spotted it before.

Could we increase our space-program spending and make it better ?

 

[silylene]

This could be a human race life killing asteroid, if it hits, with the most likely collision in the next 100 yrs on Jan 13, 2012. (Palermo scale -1.17 for that date).

However, the impact probability is only 1 in 37 million. The Palermo scale is high because of the size and KE the collision would have (as MW explained). Also the arc only has 25 observations spanning 4.7 days. Several months of observational data are needed before I will get worried. Almost always, more data refines the orbit, and this reduces the probable risk.

I predict that the date, 2012, will be popularized very soon, as the nutcases become aware of HC82. (why would this have to be 2012 of all years?)

 

[R1]

January 13, of 2012 is also Friday, as is the approach of Apophys on Friday, April 13, 2029.

 

[silylene]

Geesh, it would have to be Friday the 13th in 2012 !!

Another two data points from observations were added, which increased the observational ARc to over 5 days. The additional data has decreased the Plaermo Scale to -2.16/-2.23 (JPL Sentry / NEODYS). The chance of a strike is now 1 on 294 Million.

 

[R1]

If this is a comet remnant, could it have ice or other materials that would cause it to wobble out of
its estimated trajectory, however slightly ?

 

[MeteorWayne]

It could, though no signs of a coma have been detected yet at > 1 AU. With a perihelion close to Mercury's orbit, it certainly is possible if there's any left. I'm sure if there are any favorable opportunities we will monitor it on it's next visit to the inner solar system in 2012.

 

[MeteorWayne]

from the OP article:

astronomers think they should have spotted it before.

Could we increase our space-program spending and make it better ?

We're actully doing quite well over the last few years, and when PANSTARRS goes online, we'll be dicovering asteroids at rates that may break the data bank system at the Minor Planet Center.

 

[silylene]

With newer data, just a few hours ago all remaining impact solutions were removed from HC82. This asteroid will not collide with earth in the next several centuries.

 

[R1]

That's if nothing bothers it.

Submarines and satellites sometimetimes collide. Spacerocks may also collide, from time to time, I guess.