Category: Extrasolar Planets

Before Neptune was discovered in the 1840s, astronomers predicted its location based on how it was interacting with Uranus. Once again, this technique was used to find a planet, but this time orbiting a star 200 light-years away. It turns out planets like to be packed together in star systems. Find a gap, and you might have discovered a planet.

Astronomers from the University of Arizona in Tucson announced their findings today at the meeting of the American Astronomical Society in Austin.

Rory Barnes, a post-doctoral associate at UA’s Lunar and Planetary Laboratory, and a team of colleagues studied the orbits of several planetary systems. They found that the planets are generally packed as close together as possible without actually gravitational disrupting each other – if you get them any closer, planets will be kicked inward or outward from the system. This is called the Packed Planetary Systems hypothesis.

“The Packed Planetary Systems hypothesis reveals something fundamental about the formation of planets,” Barnes said. “The process by which planets grow from clouds of dust and gas around young stars must be very efficient. Wherever there is room for a planet to form, it does.”

The researchers studied the orbits of several planetary systems and noticed that there was a big gap between two planets orbiting the star HD 74156. So if their hypothesis was correct, there should be a planet orbiting in between the gap.

“When I realized that six out of seven multi-planet systems appeared packed,” Barnes said, “I naturally expected that there must be another planet in the HD 74156 system so that it, too, would be packed.”

With this prediction in hand, a team of astronomers from the University of Texas made careful observations of the HD 74156 system, looking for the theorized planet.

And guess what… they found it!

With this prediction confirmed, Barnes and his colleagues also predicted that there should be another planet orbiting around 55 Cancri. This was found by a different team of astronomers.

The researchers have predicted a specific planet orbiting a third star, but so far they haven’t found it.

But as more planetary systems are discovered, the Packed Planetary Systems hypothesis will fill in the holes. Astronomers will know where to look for more planets.

Original Source: University of Arizona News Release

Newly forming planetary systems follow a routine. They collapse down from a cloud of gas and dust to form a central star and orbiting planets. But astronomers have found two unusual stars that went through a second phase of planetary formation, hundreds of millions or even billions of years after the first.

The announcement was made by Carl Melis, an astronomy graduate student at UCLA, at the 211th meeting of the American Astronomical Society held in Austin, Texas.

“This is a new class of stars, ones that display conditions now ripe for formation of a second generation of planets, long long after the stars themselves formed,” Melis said.

The two bizarre stars are known as BP Piscium, in the constellation Pisces, and TYCHO 4144 329 2, in the constellation Ursa Major. They have characteristics similar to young stars, such as the rapid accretion of gas, extended disks of material, infrared emissions of radiation, and even jets.

They may act young, but these stars are very old. The astronomers measured the quantities of lithium in the stars; an element which is consumed when stars get older. If they were young, they would still have their reserves of lithium, but they have very little of it left.

So you have older stars behaving like young stars; what happened?

The researchers think that these stars were once part of a binary system where a solar-mass star was matched with a much less massive star. The more massive star ran out of fuel first and ballooned up as a red giant, engulfing the smaller star. At this point, the smaller star would actually be orbiting inside the envelope of the red giant, forcing material out into space, while slowly spiraling inward to meet its destruction.

This ejected material would actually contain the building blocks of terrestrial planets, and so, the planetary formation process would get going all over again. The size of the new planets that could form would depend on how much material was ejected during this red giant phase.

Original Source: UCLA News Release

Our early Solar System was a violent place. For hundreds of millions of years, large planetoids smashed together, forming larger and larger planets. This same process is happening in other star systems right now. In fact, astronomers have discovered a system where a Neptune-sized object and a Jupiter-sized object might have just smashed together. Ouch.

This newly discovered planet orbits a 25-Jupiter-mass brown dwarf located about 170 light-years away. Computer models show that the brown dwarf is very young, probably only 8 million years old. This means that its planetary companion should be the same age.

And here’s why they think it’s the result of a massive collision. At its current age, the planet should have cooled down to a temperature of about 1000 Kelvin. But recent observations show that it’s actually around 1600 Kelvin. So something heated it up.

That something might have been a planetary collision.

“Most, if not all, planets in our solar system were hit early in their history. A collision created Earth’s moon and knocked Uranus on its side,” explained Eric Mamajek, of the Harvard-Smithsonian Center for Astrophysics. “It’s quite likely that major collisions happen in other young planetary systems.”

An object this size should radiate its heat away over the course of 100,000 years, so this collision must have happened relatively recently.

That’s a pretty exciting possibility, but there are some more conservative possibilities as well. Other astronomers have proposed that the planetary companion is actually much smaller, only the size of Saturn. So it would have a smaller surface area radiating all the detected energy.

If this technique works out, astronomers could just take the temperature of planets in young star systems, and calculate just how long it’s been since they were impacted. “Hot, post-collision planets might be a whole new class of objects we will see with the Giant Magellan Telescope.”

Original Source: CfA News Release

The discovery of Gliese 581 was one of the most exciting moments in extrasolar planetary researcher. Astronomers found an Earth-massed planet orbiting within the habitable zone of a distant star. This would mean that liquid water could be on its surface – and maybe life. Now there’s even more evidence that Gliese 581 is living up to the speculation. Astronomers have published two independent studies this week, claiming that there are least 2 Earthlike planets orbiting the star within the habitability zone.

The first team, led by Franck Selsis, computed the properties of planetary atmospheres at various distances from the star. As we’ve seen with Venus, Earth and Mars in our own Solar System, your distance from the star matters a great deal. Get too close, and the water is vaporized and blown out into space. Get too far away and your carbon dioxide can’t trap in enough heat to keep the planet warm. You want to be just right.

Selsis and his team calculated that the inner boundary of this habitable zone around Gliese 581 should be somewhere between 0.7 and 0.9 astronomical units (an AU is the distance from the Earth to the Sun). And the outer zone should be between 1.7 and 2.4 AU. At least one planet orbiting Gliese 581 falls within this range.

The second team used a different technique to calculate habitability. They studied a narrower region where Earth-like photosynthesis is possible. For the super-Earths thought to be orbiting Gliese 581, they calculated the sources of atmospheric CO2 (volcanos and ridges) and then the potential sinks through weathering. If a planet’s too old, if might not be active any more, and wouldn’t release enough CO2 to keep the planet warm.

Once again, the age of the planets, and therefore the amount of carbon dioxide, is within this region of habitability.

Thanks to this new research, the planets orbiting Gliese 581 are primary targets for future planet hunting observatories, such as ESA’s Darwin and NASA’s Terrestrial Planet Finder. These observatories should be able to directly measure the atmospheres of these planets, and determine if they harbour life.

A third paper on the topic has recently been accepted for publication in the journal Astronomy and Astrophysics. In this, another team of researchers have studied the long term orbits of planets going around Gliese 581. Here you want stability, without highly eccentric orbits that might cause extreme warm and glacial eras. Once again, the planets around Gliese 581 are surprisingly stable.

Things are looking really hopeful. Now we just need someone to uncancel the Terrestrial Planet Finder.

Original Source: Astronomy and Astrophysics

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