Category: Extrasolar Planets

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

Our Solar System has 8 planets, but another, 55 Cancri, is catching up fast. Astronomers today announced the discovery of a 5th planet in the system, located 41 light-years away. This newly discovered planet weighs in with 45 times the mass of the Earth, and might look similar to Saturn in composition and appearance. But the news gets better, it’s in the star’s habitable zone, and could have water-covered moons.

The discovery of a 5th planet around 55 Cancri was made by astronomers from UC Berkeley, and several other collaborating universities, with funding from NASA and the National Science Foundation. Their research will appear in an upcoming issue of the Astrophysical Journal.

Astronomers used the radial velocity technique to find the planets. This is where the velocity of the star is carefully measured. Periodic changes in this velocity mean that a large planet’s gravity is yanking the star back and forth. In this case, the discovery was even more difficult, because there were already known planets in the system, polluting the data.

“It is amazing to see our ability to detect extrasolar planets growing,” said Alan Stern, associate administrator for the Science Mission Directorate at NASA Headquarters, Washington. “We are finding solar systems with a richness of planets and a variety of planetary types comparable to our own.”

Perhaps the coolest part of this whole discovery: the planet orbits its parent star once every 260 days. This places it within its star’s habitability zone, where liquid water can be present. It’s a little closer than our Earth is to the Sun, but its star is also a little fainter, so it all evens out.

Obviously, this rules out the planet itself, but it could have a collection of moons, just like Saturn. Instead of Saturn’s icy moons, this 5th planet of 55 Cancri could have ocean moons.

Finding this planet was an enormous challenge. The discoverers have been making observations of 55 Cancri for 18 years, before the first extra solar planets were ever found. They had to make more than 320 velocity measurements to disentangle the 5 planets from the data.

Original Source: NASA/JPL News Release

You know the science of planet hunting is getting mainstream when there’s very little fanfare for the discovery of 3 new extrasolar planets with the size of Jupiter. 3 new planets people! They’re named WASP-3, WASP-4, WASP-5, and were discovered by a European team of astronomers using observatories in South Africa and the Canary Islands.

The new planets were discovered using the SuperWASP instruments. These are high speed cameras affixed to two telescopes: SuperWASP-North at Roque de los Muchachos Observatory on the island of La Palma in the Canaries and SuperWASP-South at the South African Astronomical Observatory, South Africa. Both instruments are equipped with a detailed CCD camera array capable of monitoring up to 400,000 stars every minute.

They’re watching to see if any of those stars vary in brightness. If a star does get brighter and dimmer over a regular period, the astronomers can then determine if a planet is passing in front – an event known as a transit (or eclipse). Just by measuring the dimming, astronomers can then determine the size of the planet, and even some of its chemical constituents.

With this latest discovery, the three new planets all contain roughly the mass of Jupiter, but orbit much closer into their parent stars. They complete an orbit every 2 two days.

According to one of the discoverers, Dr Don Pollacco of Queen’s Astrophysics Research Centre, “these are among the shortest orbital periods yet discovered. Being so close to their star, the surface temperatures of the planets will be more than 2000 C, so it is unlikely that life as we know it could survive there. However, the finding of Jupiter-mass planets around other stars supports the idea that there are also many Earth-sized planets waiting to be discovered as the technology employed by astronomers improves.â€?

Even a relatively tiny planet the size of the Earth should visibly dim the light from a star as it passes in front. This is an exciting technique that should just get better and better over time.

Original Source: University of St. Andrews News Release

Science fiction writers have been imagining other worlds for years, and now they’re going to get a little scientific help, thanks to NASA. The agency recently modeled a range of roughly Earth-sized planets, from the familiar to the exotic. Instead of thinking just about planets with Earthlike characteristics, they imagined every possible kind of planet that might exist around other worlds. This should keep the writers busy.

We’re not talking about familiar looking planets, with strange surface features and aliens with pointed ears here, we’re talking about the very extremes of planetary formation: pure water ice, carbon, iron, silicate, carbon monoxide, and silicon carbide, and others which could be mixtures of these various compounds.

The team eventually came up with 14 different types of solid planets that might exist. “We have learned that extrasolar giant planets often differ tremendously from the worlds in our solar system, so we let our imaginations run wild and tried to cover all the bases with our models of smaller planets,” said NASA’s Marc Kuchner. “We can make educated guesses about where these different kinds of planets might be found. For example, carbon planets and carbon-monoxide planets might favor evolved stars such as white dwarfs and pulsars, or they might form in carbon-rich disks like the one around the star Beta Pictoris. But ultimately, we need observations to give us the answers.”

They calculated how gravity should compress planets of varying composition. For example, a pure water planet would be about the same size as the Earth, while an iron planet would be a third our size.

The researchers are hoping their calculations will help future planet hunters identify new discoveries. When powerful planet finders, such as ESA’s Corot mission start making discoveries, astronomers will be working hard to categorize what they’re looking at, based only on the mass and size. Even more powerful observatories, such as the James Webb Space Telescope will let astronomers actually measure the chemical constituents of a planet, and help reveal if we’re looking at a sphere of carbon or water ice.

Their paper will appear in the October 20th issue of the Astrophysical journal.

Original Source: NASA News Release

When a star like our own Sun nears the end of its 10 billion year life, it expands up into a red giant, consuming any planets foolish enough to orbit closely. But what happens to the more distant planets? Astronomers have discovered just such a planet, orbiting a red giant star. Perhaps this gives us hope for the fate of our own planet Earth, when the Sun expands too. Not so fast.

An international team of astronomers from 15 different countries announced the planetary discovery, and their article will be published in the September 13th edition of the journal Nature.

The planet is called V 391 Pegasi b, and before its parent star transformed into the red giant we see today, it orbited at roughly the same distance as the Earth. As the star expanded, its centre of gravity changed, and the planet’s orbit spiraled outward, keeping pace with the changing star. Although the star now engulfs a distance comparable between the Sun and the Earth, the planet is now out past the orbit of Mars; takes 3.2 years to complete a full year.

So does this mean the Earth’s safe? Not so fast. Here’s one of the researchers, Steve Kawaler from Iowa State University:

“We shouldn’t take too much heart in this – this planet is larger than Jupiter, so a smaller planet like the Earth could still be vulnerable. As far as our planets are concerned, we expect Mercury and Venus to disappear in the Sun’s envelope, whereas Mars should survive. The fate of the Earth is less clear because its position is really at the limit: it appears more likely that the Earth will not survive the red giant expansion of the sun either, but it is not for sure.”

Finding this planet was incredibly laborious work. It took seven years of observations and calculations to confirm its existence. It also marks the first time that a new technique was used to discover planets. Traditionally, astronomers measure the change in a planet’s velocity as it’s yanked back and forth by the gravity of a large planet using a technique called spectroscopy, where the spectrum of its light shifts. In the case of V391 Pegasus b, the astronomers measured small variations in timing of light coming from the star to determine its velocity.

Original Source: University of Delaware News Release

Ever wonder how the Earth got its oceans? Well, new data gathered by NASA’s Spitzer Space Telescope could provide a clue. The telescope imaged a planetary disk forming around a young star, surrounded by a cloud of water vapour. This water is raining down right into the dusty disk where planets are thought to form.

Now that’s convenient.

The discovery appears in the August 30th edition of the journal Nature. According to the discovering astronomers, there’s enough water vapour located in the star system NGC 1333-IRAS 4B, located about 1,000 light-years away, to fill up the oceans on Earth 5 times over.

Astronomers used to believe that Earth’s water arrived early on in our Solar System’s formation in the form of icy comets. The early Earth was bombarded by comets large and small, and our oceans slowly built up over time. But this research indicates that water falling as ice will actually vapourize as it arrives from the stellar envelope to its disk.

The discovering team studied a total of 30 stellar embryos, using Spitzer’s infrared spectrograph, which can peer through obscuring dust. Of all the systems they analyzed, only one had such a strong signature of water. The vapour was easy to spot for Spitzer because when the ice falling from the envelope into the planet-forming disk, it heats up, glowing with infrared light.

Is this a rare situation? The astronomers believe the water signature was so bright because the star system is perfectly lined up for Spitzer to be able to see its bright core. It’s also probably that this phase of planetary formation is very short lived, so the other systems have already gone through this phase, or will do so shortly.

Original Source: NASA/JPL/Spitzer News Release