[meteorite-list] Jupiter Hit By An Asteroid/Comet on March 17?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 29 Mar 2016 10:28:22 -0700 (PDT)
Message-ID: <201603291728.u2THSMPc006503_at_zagami.jpl.nasa.gov>

http://www.slate.com/blogs/bad_astronomy/2016/03/29/jupiter_hit_by_asteroid_or_comet_in_march_2016.html

Jupiter Got Whacked by Yet Another Asteroid/Comet!
By Phil Plait
March 29, 2016

[Image]
Wham! From 665 million km away an asteroid or comet was seen impacting
Jupiter (arrowed). Three moons are visible too: From left to right, Europa,
Ganymede, and Io.
John McKeon, from the video

On March 17 an amateur astronomer in Modling, Austria, was taking video
of Jupiter using a 20 cm telescope. This is a common technique to capture
thousands of frames of an object, so that the best parts of each frame
can be teased out to create a high-resolution image, removing the distorting
effects of the atmosphere.

But he got more than he expected. At 00:18:33 UTC he captured what looks
very much like the impact of a small comet or asteroid into Jupiter! Watch,
and keep your eyes on the upper right part of Jupiter's limb (it might
help to change the playback speed to 1/2):

[Video]

Whoa. The flash is very brief but definitely there. When I first saw the
video I thought it looked very much like an impact, but it could have
also been a reflection inside the telescope, or many other non-impacty
things.

To confirm it, what we really need is a second observer who happened to
be looking at the same time.

Voil:

[Video]
That was taken by John McKeon, observing with a 28 cm 'scope in Swords,
just north of Dublin, and the timing is consistent with what's seen
in the first video. I would say this is very strong evidence for an actual
impact.

As to what did the impacting, that's less clear. It could be either
a small asteroid or a small comet. Given how brief the flash was, and
how bright, I'm sure it wasn't terribly big, probably in the tens-of-meters
wide range. I know that sounds small, but remember, Jupiter has ferocious
gravity, and velocity is critical here! The energy released by an object
slamming into another depends linearly on the mass (double the mass, double
the energy), but on the square of the velocity: double the velocity, quadruple
the energy.

On average (and ignoring orbital velocity), an object will hit Jupiter
with roughly five times the velocity it hits Earth, so the impact energy
is 25 times as high. The asteroid that burned up over Chelyabinsk, Russia,
in 2013 was 19 meters across, and it exploded with the energy of 500,000
tons of TNT.

Now multiply that by 25, and you can see how it doesn't take all that
big a rock to hit Jupiter for us to be able to see it from Earth.

Incidentally, at these huge speeds, hitting the atmosphere is like slamming
into a wall. A lot of people get understandably confused how an asteroid
can explode due to air, but the pressures involved as it rams through
the atmosphere at these speeds are ridiculously huge. The air and rock
heat up, the rock starts to fall apart, and each chunk then gets hot,
and so on, creating a very rapid cascade that releases the energy of motion
in just a second or two.

Bang. Very, very big bang.

Jupiter gets hit a lot. We've seen impacts like this before, many times
in fact! The most famous is the string of impacts from the comet Shoemaker-Levy
9 in 1994, which hammered the planet over and again as the comet, broken
into a dozen separate pieces by Jupiter's gravity, slammed into the
planet and exploded. In 2009 something relatively big hit the planet (and
Hubble caught the aftermath). It was hit again in June 2010 (with a cool
color photo this time), and then again in August 2010. A repeat performance
was held in September 2012.

[Image]
Image from the June 2010 impact.
Anthony Wesley

Looking over these observations, it seems that on average Jupiter gets
hit by something big enough to see from Earth about once per year. Mind
you, we miss ones that happen on the far side of the planet, or when Jupiter
is too close to the Sun to be observed.

I'll note that Jupiter has always been getting hit, but the uptick in
detections is because our technology is getting better and less expensive.
You don't need a zillion dollar observatory to catch something like
this; an off-the-shelf telescope and video camera can do the trick. I'm
not saying it's easy; astrophotography still takes skill and patience.

But there is no lack of talented and eager amateur astronomers out there
willing to put in the time. If I had had tech like this when I was in
high school and observing in my yard every clear night, I'd have been
videoing Jupiter every night it was up! The hard part, though, is actually
finding the event in the footage. As you can see, it only lasts for a
second or so, which might be hard to spot in hours of footage. Kudos to
the two (so far) who did manage to see it.

So it's worth the call: If you happened to be taking video of Jupiter
that night, please let me know. I don't think any big observatories
will be following up with this event (it wasn't big enough to leave
any visible damage in the cloud tops), but the more info we have on it,
the better.
Received on Tue 29 Mar 2016 01:28:22 PM PDT