Author: Fraser Cain

To destroy a terrestrial planet, you need the Death Star. But what will you do if you want to take out a gas giant? No mere superlaser is going to get the job done. But if you can get the gas giant close enough to its parent star, you should just be able to make it evaporate. How close? According to researchers from University College London, get a planet twice as close as Mercury to its parent star and it’s a goner (in a few billion years).

But whoa you say, haven’t astronomers found planets orbiting well within this distance? They certainly have. In fact, HD 209458b is 70% the mass of Jupiter and orbits its parent star about 12% the orbital distance of Mercury. And it’s evaporating as we speak.

Okay fine, it doesn’t destroy a planet in such a spectacular fashion as blasting it with a superlaser, but you can rest assured, its fate is sealed. Queue the maniacal laughter…

The research was carried out by Tommi Koskinen from University College London, and published in this week’s edition of the journal Nature.

According to Koskinen and his colleage, Professor Alan Aylward, they used some sophisticated new modeling tools to get at their calculations. They used 3D-modeling techniques to see the whole heating process as the planet gets closer to the parent star. Their model includes the powerful supersonic cooling winds that have been detected on other planets.

Within 0.15 astronomical units of the star is the point of no return for a gas planet. Within this radius and molecular hydrogen in its atmosphere becomes unstable and temperature regulating processes become overwhelmed. The planet’s atmosphere then begins to heat up uncontrollably.

Temperatures on the planet will rise from 3,000 degrees Celsius to more than 20,000 degrees. At this point its atmosphere begins boiling off into space.

It’s not a quick process. Planets at this distance will start losing material very slowly, and will probably still survive for billions of years.

You’ll have to be a very patient evil space emperor to destroy gas giants this way.

Original Source: UCL News Release

Good timing. Just as Nick was mentioning how astronomers might be able to detect vegetation on extrasolar planets, we get this discovery: a ground based observatory has measured the atmosphere of an extrasolar planet for the first time. That holy grail of detecting the atmosphere on an Earth-sized world is getting closer and closer.

In a new journal article published in an upcoming issue of Astrophysical Journal Letters, astronomer Seth Redfield and colleagues report on their discovery.

The planet they’re studying orbits star HD189733, located about 63 light-years away in the constellation Vulpecula. It was originally discovered back in 2004. Unfortunately, this planet isn’t anything like the Earth; it’s actually about 20% more massive than Jupiter, and orbits its parent star 10 times closer than Mercury. Needless to say, it’s a hot world.

From our perspective here on Earth, HD189733b passes in front of its star on each orbit. As the planet “transits” across the star, it dims the light slightly. Furthermore, sunlight passing through its atmosphere can be measured distinctly from the star itself. The planet blocks about 2.5% of the star’s total light, and the atmosphere blocks an additional 0.3%.

And this was the technique that Redfield and his team used to measure the atmosphere. “Take a spectrum of the star when the planet is in front of the star,” explains Redfield. “Then take a spectrum of the star when it’s not. Then you divide the two and get the planet’s atmospheric transmission spectrum. Each time the planet passes in front of the star the planet blocks some of the star’s light. If the planet has no atmosphere, it will block the same amount of light at all wavelengths. However, if the planet has an atmosphere, gasses in its atmosphere will absorb some additional light.”

The atmosphere of an extrasolar planet has only been measured once before, using Hubble’s Space Telescope Imaging Spectrograph (STIS). Unfortunately, this instrument broke shortly after the previous detection. Without the help of Hubble, Redfield and his team needed to come up with another solution, so they switched to the Hobby-Eberly Telescope.

In the end, they made hundreds of observations spread out over a year taken under various conditions. They were able to remove the contamination of the Earth’s atmosphere from their observations, and come up with a good analysis of the planet’s atmosphere.

This is great, but it’s just a start. The real prize will come with astronomers are able to spot Earth-sized planets orbiting other stars, and measure their atmospheres. If they find large quantities of oxygen in the atmosphere, that’s a good candidate for life.

Original Source: McDonald Observatory News Release