Thursday, May 31, 2007

Worlds, by the Double Handful

Like an adventurer spilling a silk bag full of doubloons across a table, the California planet search team has revealed 28 new extrasolar planets, the largest haul of them yet. I saw this in the LA Times a few days ago, but only got the confirmation from the team's website. They still aren't up on the Extrasolar Planets Encyclopaedia, so I can't say much about them beyond what is in the news release. (The Encyclopaedia is run by the Paris Observatory - a whiff of rivalry in their not rushing to post?)

Three of them orbit stars considerably larger and brighter than the Sun - combined with six planets orbiting other such stars, discovered earlier, they hint at distinct patterns in what sorts of planets form around what what kinds of stars. In short, bigger stars may tend to have bigger planets, orbiting farther away. Which is about what we'd expect, but with exoplanets, even finding the expected is a surprise, because so often we find the unexpected.

The news release also had new information on a planet previously discovered orbiting the star Gleise 436.* Already detected by gravitational wobble, it now has also been (indirectly) seen in transit, passing directly in front of the star, allowing the astronomers to pin down its size and mass. (Previously they had only an estimate of its mass, and only the sheerest guess as to its size.) It is four times the size of the Earth and 22 times as massive - about the same size as Neptune, and slightly heavier. However, it orbits its parent star at 0.03 AU, about a thousand times closer than Neptune orbits the Sun. Though Gleise 436 is a dim lamp among stars, a planet that close in the planet must be hot.

We can also guess, or the astronomers can, that it has a similar composition to Neptune - about half of it being ice, or whatever form good old H2O takes when it is subjected to enormous heat and pressure thousands of kilometers deep inside a planet.

I like this planet, because it brings us even closer to the notion of a "water giant," even if this one is more like a permanent boiler explosion, held down by its own sheer weight.

* Gleise 581 already figured in this blog, as putative home star of a "super Earth." Apparently someone named Gleise once catalogued a whole bunch of mostly unspectacular stars, which turned out to be just the sort planet hunters like. Henry Draper catalogued even more of them, which is why so many planets orbit stars named HD followed by a number.

3 comments:

Nyrath said...

Wilhelm Gliese and Henry Draper cataloged dim stars. These tend to be nearby (otherwise they are too dim to be seen). And current planet finding techniques require the stars to be nearby. That's why so many of the planet bearing stars start with the name "Gliese" or "HD".

Rick said...

Alas, I don't remember many Gleise or HD stars in SF - when we were growing up it was always Top Forty stars like Alpha Centauri or Epsilon Eridani.

In Time For The Stars, the "Elsie" does make a stop at a star described as so dim it only has a catalog number - probably Gleise or HD something. But even Heinlein doesn't have any of the story happen there; he only mentions the stop in passing.

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