Tuesday, February 4, 2014

Of distant worlds

Recent years have offered a steady stream of exciting exoplanetary news. Here's a smattering of such findings I've collected since my last astro-centric post.

That dot? Beta Pictoris b.
Let's begin with (IMO) the most visually stunning item, even though very few pixels are involved: an exoplanet, 63 light-years distant, directly imaged by a ground-based telescope. See (from The Register) "ALIEN WORLD Beta Pictoris snapped by Earth's Gemini 'scope." (That's sloppy headline writing: the star, Beta Pictoris, is not viewed. It's intentionally occluded lest its glare wash out the planet. The world is Beta Pictorus b.)

How was this bit of astronomical legerdemain accomplished? With adaptive optics, a serendipitous spinoff from research into antimissile lasers. Adaptive optics is a wondrous technology.

Next up: different cleverness. The Kepler observatory identified, sans direct imaging, many an exoplanet. The method: spotting the slight dips in brightness as distant planets transited distant stars. With the failure of two reaction wheels, the orbiting telescope, alas, can no longer point steadily enough to continue making such precise observations.

Or so it was believed ...

Kepler observatory
It now appears that, positioning the spacecraft to exploit the solar wind, "NASA's Ailing Kepler Spacecraft Could Hunt Alien Planets Once More with New Mission." Space.com reports that: "During a 30-minute pointing test in late October, for example, Kepler captured an image of a distant star field that was within 5 percent of the image quality achieved during Kepler's original mission."

(February 6th update: A mere two days after this post, the proof is in: Kepler can go back to work. See, from New Scientist: "NASA's revived exoplanet-hunter sees its first world.")

And while we're on the topic of exoplanets, see (from Sci-News.com) "HD 106906b: Unique Super-Jupiter Exoplanet Discovered."

HD 106906 b
Why unique? Because one doesn't expect to find a gas giant orbiting so far from its star. The farther from the (proto-)star one gets, the less gas and dust (says the theory) the original proto-planetary disc provided for planet-building. And so, in our solar system, the largest gas giant, Jupiter, is the closest to the sun. Saturn, the next largest gas giant, is the next closest. Beyond Neptune the bodies orbiting the sun are small rocky and/or icy objects like Pluto (and other, lesser known, Kuiper Belt Objects).

The anomalous exoplanet, HD 106906 b, weighs in at 11 times the mass of Jupiter and orbits its hosting star at ~20 times Pluto's orbit.

By the same theory of planetary formation, of course, Neptune could never have formed where it's observed. So, it is believed, Neptune didn't form where it now orbits, but migrated outward in the complex dance of solar-system formation and maturation. The "hot Jupiter" exoplanets that are often detected (perhaps because they're the easiest to detect) also could not have formed where they are detected. They, it would seem, migrated inward after forming. Yet other planetary mass objects (not technically planets because they don't orbit a star) as large as gas giants have been detected (by gravitational micro-lensing) free-floating in interstellar space. In theory, a star could capture such a planetary mass object into orbit -- making it a planet.

Do any of these scenarios explain HD 106906 b? The jury is out.

We'll end today's survey of exoplanet news with "Weight of the World: New Technique Could Weigh Alien Planets." ("Weigh" is an inexact term, though I concede the value of brevity in a headline. The point is to determine the mass of exoplanets.)

The usual method for estimating an exoplanet's mass is via the wobble that mass induces in the position of its star. Alas, many an exoplanet isn't massive enough, and/or doesn't orbit close enough to its sun, to produce a measurable-from-Earth stellar wobble. The new method relies upon the gravitational effects of a planet's mass on its own atmosphere. The more massive a planet, the more quickly its atmosphere thins with altitude -- and that effect can (in theory) be exploited by observing stars shining through an exo-planetary atmosphere.

Next time ... observations closer to home.

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