Tag: comets

One hundred days to wake-up for Europe’s Rosetta comet probe.

8:26 am

One hundred days to wake-up for Europe’s Rosetta comet probe.

Rosetta was launched on 2 March 2004, and through a complex series of flybys – three times past Earth and once past Mars – set course to its destination: comet 67P/Churyumov–Gerasimenko. It also flew by and imaged two asteroids, Steins on 5 September 2008 and Lutetia on 10 July 2010. In July 2011 Rosetta was put into deep-space hibernation for the coldest, most distant leg of the journey as it travelled some 800 million kilometres from the Sun, close to the orbit of Jupiter. The spacecraft was oriented so that its solar wings faced the Sun to receive as much sunlight as possible, and it was placed into a slow spin to maintain stability.

Now, as both the comet and the spacecraft are on the return journey back into the inner Solar System, the Rosetta team is preparing for the spacecraft to wake up.
Rosetta mission milestones 2014-2015 Rosetta’s internal alarm clock is set for 10:00 GMT on 20 January 2014.

The first images are expected back in May 2014.

Posted as we approach the Arkansas-Texas border.

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Scientists in Egypt have found what they think is evidence of a comet impact from 28 million years ago.

10:39 am

Scientists in Egypt have found what they think is evidence of a comet impact from 28 million years ago.

The best part however is this:

At the centre of the attention of this team was a mysterious black pebble found years earlier by an Egyptian geologist in the area of the silica glass. After conducting highly sophisticated chemical analyses on this pebble, the authors came to the inescapable conclusion that it represented the very first known hand specimen of a comet nucleus, rather than simply an unusual type of meteorite.

Assuming this claim is confirmed it is a very significant discovery. As far as I know, no other specimens from a comet nucleus have been identified previously.

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Comet ISON has now brightened to 11th magnitude as it approaches its flyby of Mars.

9:41 am

Comet ISON has now brightened to 11th magnitude as it approaches its flyby of Mars.

The story above is hopeful the comet will put on a show in November, but I am increasingly doubtful. To be even visible to the naked eye it must brighten to 6th magnitude, and it appears to be brightening far slower than expected.

Posted as we drive through El Paso, Texas.

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Linking mass extinctions to the Sun’s journey in the Milky Way

12:53 pm

The Sun's orbit in the Milky Way

In a paper published today on the Los Alamos astro-ph preprint service, astronomers propose that as many as eleven past extinction events can be linked to the Sun’s passage through the spiral arms of the Milky Way. (You can download the paper here [pdf].)

A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events. Furthermore, we identify five additional historical mass extinction events that might be explained by the motion of the Sun around our Galaxy. These five additional significant drops in marine genera that we find include significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago. Our simulations indicate that the Sun has spent ~60% of its time passing through our Galaxy’s various spiral arms.

The figure on the right, from their paper, shows the Sun’s orbit in red over the last half billion years. The Sun’s present position is indicated by the yellow spot, and the eleven extinctions are indicated by the circles.

There are obviously a great deal of uncertainties in this conclusion. Most significantly, the shape and history of the Milky Way remains very much in doubt, especially since we reside within it and cannot really get a good look at it. Though in recent years astronomers have assembled a reasonable image of the galaxy’s shape — a barred spiral with two major arms and several minor ones — this picture includes many assumptions that could very easily be wrong.

Nonetheless, the paper’s conclusions are interesting.
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Comet ISON has come out from behind the Sun, and it looks like it will not produce a grand show for us later this year.

10:53 am

Comet ISON has come out from behind the Sun, and it looks like it will not produce a grand show for us later this year.

There will be a lot of stupid commentary criticizing astronomers for hyping this comet, all unfair. The comet had the strong possibility of being spectacular. Astronomers pointed that out, being as hopeful as everyone to see a bright and beautiful comet grace our night skies for a few months. That this is not turning out to be so is not their fault.

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“Comet of the Century”? We’ll soon find out.

9:29 am

“‘Comet of the Century’? We’ll soon find out.”

This article, as well as a bunch of others published this week about Comet ISON, suggest to me that the comet is going to be a dud. These articles all are suggesting that we won’t know if the comet will be as bright as hoped until after it flies around the sun. This is absolutely wrong. As the comet drops down towards the sun it should heat up and begin brightening, producing a tail. This is what all comets do. If it doesn’t brighten on its journey in, then it won’t be bright on its journey out.

That the authors of these articles don’t know that, or are hiding it, is simply bad journalism. Moreover, this effort to spin the comet’s dimness now suggests that the comet is now far dimmer than hoped, which strongly suggests it will remain that way.

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The lingering echo of Comet Shoemaker-Levy in the atmosphere of Jupiter.

7:32 pm

The lingering echo of Comet Shoemaker-Levy in the atmosphere of Jupiter.

The Herschel observations, together with heat maps provided by NASA’s Infrared Telescope Facility on Mauna Kea, showed the researchers that the Jovian stratosphere was 20° to 30°F (10° to 15°C) warmer than it would be if completely dry. One question is whether the stratospheric warming results from the gentle, continuous infall of interplanetary dust particles, which would be warmed by sunlight as they linger high up. Cavalié and his colleagues believe IDPs create some of the infrared emission but cannot explain it all. Further, a continuously supplied source would migrate to lower depths, yet most of the emission is too high up, at pressures less than 2 millibars. And while the amount of water is roughly constant across the southern hemisphere, the emission gradually weakens northward until it’s less than half as strong. It’s not simply that Jupiter’s bottom half is hotter — there’s just more water down there. As the researchers note, “At least 95% of the observed water comes from the SL9 comet and subsequent (photo)-chemistry in Jupiter’s stratosphere according to our models, as of today.

Taken together, they conclude, these observations offer “clear evidence that a recent comet … is the principal source of water in Jupiter. What we observe today is a remnant of the oxygen delivery by the comet at 44°S in July 1994.”

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Observations of Comet Hale-Bopp at 30 AU

8:52 pm

In a paper published tonight on the Los Alamos astro-ph preprint website, astronomers described new observations of Comet Hale-Bopp at a distance of 30 astronomical units, or 2.8 billion miles, from the sun. Their conclusions:

  • These observations were the most distant detection of any known comet.
  • The comet’s starlike appearance and its drop in brightness since the last observations suggest that the comet has finally ceased, or is about to cease, all activity, and that they are now looking directly at the comet’s nucleus instead of the coma cloud surrounding it.
  • Nonetheless, the comet is brighter than expected, which also suggests that a thin layer of new ice covers its surface and thus increases its albedo.

To quote the paper, “Observing Hale-Bopp in a completely frozen state would be extremely important because a thick coma was constantly present during the entire appariation [Ed. the fly-by of the Sun]. The coma obscured the nucleus which was not observed directly. Lack photometric data of the bared nucleus, its size — one of the most important input parameter in activity models — remains uncertain.”

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