The sky seems to be full of interesting objects that are breaking apart. They’re always worth studying, as we learned through the impacts of the famous ‘string of pearls’ comet — Shoemaker-Levy 9 — on Jupiter in 1994. For one thing, the celestial display they afford is uncommonly interesting; for another, they are a reminder of the kinds of debris that we need to track just in case any of it turns out to be on an Earth-crossing trajectory.
No apparent chance of that with 60558 Echeclus, a 50-kilometer ‘centaur’ out beyond the orbit of Saturn. Centaurs are icy planetoids that, in the case of both 60558 Echeclus and Chiron (the first centaur to be discovered), seem to display cometary properties. 60558 Echeclus is now even more interesting with the news that a large chunk of the object seems to have broken away. The resultant dust cloud is 100,000 kilometers across as both centaur and breakaway fragment blow off dust and gas, with more coming from the fragment than the main body (and that, too, remains a mystery).
Watch the theories fly as astronomers try to figure out what caused the breakup, there being no gravitational disturbances to account for it. And watch, too, the dying comet 73P/Schwassmann-Wachmann 3. For reasons unknown, the comet’s nucleus broke into three parts in 1995. The resulting mini-comets, of which there are now at least eight, are going to pass Earth in May, closer than any comet has come in twenty years, providing an unusual visual display for the Hubble instrument, not to mention legions of amateur astronomers. The fragments will give us our first close-up look of a comet’s end and may provide an accompanying shower of meteors.
As to what made this one break up, Paul Wiegert (University of Western Ontario) has this to say:
“The most likely explanation is thermal stress, with the icy nucleus cracking like an ice cube dropped into hot soup: the comet broke apart as it approached the Sun after a long sojourn in the frigid outer solar system. If this is truly what happened, then the debris cloud should be expanding slowly, and there will be no strong meteor shower.”
No Earth-crossing danger here, either, with the closest fragment still six million miles away. But perhaps the very instability shown by these two breakups should remind us that the Solar System is still an evolving place, one where large planetary impacts can’t be ruled out. Shoemaker-Levy 9’s collision with Jupiter was spectacular indeed; such impacts on Earth would be catastrophic. Groups like the B612 Foundation, which argues the need for anticipating potential collisions and building the technologies to prevent them, continue to merit your support.
174P/Echeclus: a strange case of outburst
Authors: P. Rousselot
(Submitted on 10 Mar 2008)
Abstract: Context. More than ten Centaurs are now known to have cometary activity at large heliocentric distance (i.e. $\simeq$ 5-13 AU). Among these objects, 174P/Echeclus which showed cometary activity at 13 AU from the Sun, is a unique case, because of: (i) the amplitude of its outburst, (ii) the source of cometary activity that appears distinct from Echeclus itself.
Aims. This paper aims at investigating the physical conditions that have led to this unusual outburst. The purpose is also to quantify this phenomenon and to provide observational constraints for its modeling.
Methods. We use observations from different telescopes, performed before, during, and after the outburst. We performed the main observations on March 23 and 30, 2006, with the 8.2-m ESO Very Large Telescope and FORS 1 instrument. They consist of visible images and spectra.
Results. Our main results are: (i) a cometary source distinct from Echeclus itself that presents a brightness distribution compatible with a diffuse source; (ii) a total dust production rate Q_dust equal to about 86 kg.s^-1 and a parameter Afrho equal to 10,000cm; (iii) no emission lines (CN and C_2) can be detected in the visible range; (iv) the upper limits for the CN and C_2 production rates are about 3.8×10^25 and 10^26 molecules.s^-1 respectively; (v) we detected no Echeclus’ satellite before the outburst up to M_R equal to about 26; (vi) the upper limit for the object generating the coma is about 8 km in diameter; (vii) and we detected no cometary activity one year later, in March 2007.
Subjects: Astrophysics (astro-ph)
Journal reference: Astronomy and Astrophysics 2008
Cite as: arXiv:0803.1381v1 [astro-ph]
Submission history
From: Philippe Rousselot [view email]
[v1] Mon, 10 Mar 2008 10:15:14 GMT (2059kb)
http://arxiv.org/abs/0803.1381
The Mother of All Meteor Storms
By P. Jenniskens
Carl Sagan Center, SETI Institute
posted: 03 April 2008, 12:07 am ET
Each generation seems to get a chance, or two, to see a mind-boggling display of shooting stars one night. The most spectacular displays in my memory are the 1999 and 2001 Leonid storms. Before my time, observers swore by the 1966 Leonids, and could not stop talking about the spectacular 1933 and 1946 Draconid storms. Those were not quite as intense as the Leonids, but the Draconids moved so slowly that several were seen gliding across the sky at the same time.
In the 19th century, the most spectacular storms were the 1872 and 1885 Andromedids, which were almost as strong as the Draconids and also very slow moving. At the time, Chinese astronomers wrote: “shooting stars fell like rain.” From the counts of meteors in the west, we now estimate that rates peaked around two per second
Some years earlier, in 1846, a comet called 3D/Biela had been observed to break into at least two pieces. The pieces had drifted further apart in 1852. Based on the rate of that drift, the moment of breakup is thought to have been in either 1842 or early 1843, when the comet was far from the sun, near Jupiter’s orbit. Because of their phenomenal intensity, the Andromedid storms were believed to be caused by Earth traveling through the debris created during that breakup.
So, did we pass through the breakup debris of comet 3D/Biela? Astronomer Jeremie Vaubaillon, now at Caltech, and I decided to investigate. We calculated where the debris from 1842/43 would have ended up in the comet orbit and discovered that a breakup far from the sun does not disperse dust easily. The dust tends to keep the same orbital period, returning back at the same time. The cloud of dust tends to hang around the position of the comet, only gradually lagging the comet as a whole due to the push of solar radiation.
Full article, plus several antique illustrations, here:
http://www.space.com/searchforlife/080403-seti-mother-meteor.html
As we celebrate the start of the 40th anniversary of Apollo 11, another space
event that began 25 years after Neil, Buzz, and Mike began their journey atop a
Saturn 5 rocket took place roughly 400 million miles from Earth at the planet
Jupiter.
The comet known as Shoemaker-Levy 9, which had broken up earlier into at
least 20 main fragments thanks to Jupiter’s massive bulk, began slamming into
the gas giant world on July 16, 1994, creating huge impacts that were visible
even in amateur telescopes.
Dark areas the size of our planet appeared in a long chain across the face of
Jove for days from these impacts. The larger fragments created mushroom
clouds from their impacts that were 1,200 kilometers tall! As one might
imagine, the comet SL-9 event did a lot to get scientists, politicians, and
the general public to take the threat of celestial impacts on our world much
more seriously.
I well remember this event. I even had a chance to look at Jupiter through a
telescope on the night it all began, but I was a bit early for viewing the impact
markings. PBS Television had live extensive coverage as they often did in those
days. This was also one of the early big events shown on the very young World
Wide Web, which was born at CERN just one year earlier.
As the 25th anniversary of Apollo 11 was also happening at this time, the news
media naturally tried to combine and contrast what was happening at Jupiter then
with what took place on the Moon a quarter-century earlier. They even replayed
ABC-TV’s coverage of the Apollo 11 landing, which I videotaped. Lots of models
and hand-made drawings were used to show the audience what was going on and
just what those guys up there on the Moon and down in Mission Control were
talking about.
I recall some folks half-jokingly saying that the comet impacts on Jupiter were the
Cosmos’ way of marking and celebrating Apollo 11’s silver anniversary. I hope the
Universe doesn’t get carried away for the fiftieth anniversary a decade from now!
Lots of good images and info on comet SL-9 here:
http://seds.org/archive/sl9/sl9.html
Space Weather News For July 19, 2009
http://spaceweather.com
JUPITER IMPACT? On July 19th, a veteran observer of Jupiter in
Australia photographed a fresh dark “scar” in Jupiter’s cloudtops; the
feature resembles the Shoemaker-Levy 9 impacts of 1994.
It is possible that Jupiter has been struck anew by an asteroid or comet.
Astrophotographers around the world should train their optics on Jupiter to confirm the event and monitor its progress.
Visit http://spaceweather.com for photos and updates.
Also check this Web site on the subject:
http://www.acquerra.com.au/astro/ObsReport/jupiter-impact.html