Category: Extrasolar Planets

NASA’s Deep Impact completed its main mission. Back in July 2005, the spacecraft’s impactor carved a hole great big hole out of Comet Tempel 1, helping scientists study what lies beneath its surface. But now its time for the spacecraft to re-enter the space workforce and help discover alien worlds.

NASA recently announced that they had extended Deep Impact’s mission to fly past another comet. This time it’ll be Comet Hartley 2 on October 11, 2010. Just like the previous mission, Deep Impact – now renamed EPOXI – will be studying the surface of the comet with its suite of scientific instruments.

But between now and then, the spacecraft has some time to kill. So astronomers searching for extrasolar planets are calling it into service.

The spacecraft will be focusing its largest telescope at five stars, hoping to catch a glimpse of a planetary transit. This is where a planet dims the light from its parent star as it passes in front.

EPOXI Deputy Principal Investigator Dr. Drake Deming of NASA’s Goddard Space Flight Center in Greenbelt, Md explains the technique:

“When the planet appears next to its star, your telescope captures their combined light. When the planet passes behind its star, your telescope only sees light from the star. By subtracting light from just the star from the combined light, you are left with light from the planet,” said Deming, who is leading the search for exosolar worlds with Deep Impact. “We can analyze this light to discover what the atmospheres of these planets are like.”

This search for extrasolar planets has already begun. Deming and his team directed EPOXI to begin making observations on January 22, 2008. It’s looking at stars which are already known to have transiting planets. The hope is that these stars actually contain multiple planets. Since planets seem to orbit on the same plane, if one passes in front of the star, the rest should too. Even if the planets don’t pass perfectly in front of the star, the spacecraft might be able to detect them from the gravitational influence they have on light coming from the star.

EPOXI will be looking for transiting planets down to the size of Earth, orbiting some of our closest neighboring stars.

Original Source: NASA News Release

As space telescopes get larger and more sensitive, the search for Earth-sized worlds surrounding other stars is about to get rolling. But astronomers are going to need to know where to look. A team of researchers are working on a survey of nearby stars, calculating the habitable zones around them. When the search begins, astronomers are going to want to study these regions.

The Research Consortium on Nearby Stars (RECONS) is a survey using relatively small telescopes to study the habitable zones in the nearby stars. The team uses measurements of various stars brightnesses at optical and infrared wavelengths matched with their distances to get a sense of the stars’ habitability.

After gathering together a big list of potential candidate stars, the researchers can then categorize stars by size and temperature to find ones that might harbour life.

“Once we have good values for the temperatures and sizes of the nearby stars, we can estimate how hot planets will be at different distances from the stars,” explains Justin Cantrell, a Doctoral Candidate in Astronomy at Georgia State University. “We consider those stars that would have surface temperatures suitable for liquid water to be in the traditional habitable zone.”

The researchers were looking for habitable zones around red dwarf stars, which can be 50-90% smaller than the Sun and much cooler. The comprise 70% of the stars in the Milky Way, but they’re harder to spot because they put out less light.

They were surprised to learn that these red dwarf stars have tiny habitable zones. When they added up the habitable zones of 44 red dwarf stars nearby the Sun, they found they didn’t add up to equal the habitable zone of a single Sun like star.

So even though these red dwarfs are common, they’re not great candidates for life. Earth-type stars would need to be perfectly positioned in their tiny habitable zones to be good candidates for life.

Original Source: Georgia State University News Release

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