Tag: comets

“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.

Leave a comment

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.”

Leave a comment

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.”

Leave a comment

Stardust images of comet locate crater from Deep Impact’s impact

8:59 pm

More news from Stardust: scientists have now identified what they think is the crater produced by Deep Impact’s impact in 2005. Key quote:

The images revealed a 150-metre-wide crater at the Deep Impact collision point that was not present in 2005. The crater is a subtle feature in the images, but it appears consistently in multiple views from the spacecraft. “So I feel very confident that we did find the [impact] site,” said mission member Peter Schultz of Brown University in Providence, Rhode Island, at a press briefing on Tuesday. The crater’s features are “subdued” rather than sharply defined, like those of craters made in hard materials like rock. “The message is: This surface of the comet where we hit is very weak,” said Schultz. The crater also has a small mound in its middle, indicating that some of the material thrown up by the impact was drawn by the comet’s gravity back down into the crater, he said: “In a way, it partly buried itself.”

Leave a comment
1 … 7 8 9 10