News Article | November 17, 2015
Astronomers have discovered a rocky planet that is orbiting a small star that has many similarities to Earth and Venus. Back in May, a team of researchers using the MEarth-South telescope at the Cerro Tololo Inter-American Observatory in Chile identified the the exoplanet named GJ 1132b that is only about 39 light-years away, making it the closest exoplanet that has yet to be discovered. Published recently in the journal Nature, astrophysicists from MIT and other astronomers found that GJ 1132b is only 1.2 times the size of the Earth, has a mass about 1.6 times that of the Earth, and orbits a parent star. It takes 1.6 days for it take make a single trip around the red dwarf Gliese 1132. Just like the moon's tides are locked to our planet, the Earth-sized exoplanet also is tidally locked, which simply means it has a day and a night side, depending on which side is facing its star while in orbit. There is no denying GJ 1132b's similarities to the Earth, but it can actually pass as a cousin to another planet in our solar system, Venus. The planet orbits very close it its parent star, giving it a surface temperature much hotter than Earth's at about 440 degrees Fahrenheit. "Our ultimate goal is to find a twin Earth, but along the way we've found a twin Venus," astronomer David Charbonneau of the Harvard-Smithsonian Center for Astrophysics (CfA) said in a statement. "We suspect it will have a Venus-like atmosphere, too, and if it does we can't wait to get a whiff." While GJ 1132b is even hotter than Venus, researchers will be able to use telescopes to measure the amount of light that passes through the GJ 1132b's atmosphere, which can then be analyzed for atmospheric gases like oxygen that could give clues the alien life. But don't get too excited because the planet is even hotter than Venus, and is too close to its star for it to contain liquid water. "The temperature of the planet is about as hot as your oven will go, so it's like burnt-cookie hot," said Zachory Berta-Thompson, a postdoc in MIT's Kavli Institute for Astrophysics and Space Research. "It's too hot to be habitable—there's no way there's liquid water on the surface. But it is a lot cooler than the other rocky planets that we know of." Researchers will conduct an in-depth study of the exoplanet that has Earth and Venus-like characteristics using the Hubble Space Telescope in 2018.
The new planet, named GJ 1132b, is Earth-sized and rocky, orbiting a small star located a mere 39 light-years from Earth, making it the closest Earth-sized exoplanet yet discovered. Astrophysicists from MIT and elsewhere have published these findings today in the journal Nature. Based on their measurements, the scientists have determined that the planet is a roasting 500 degrees Fahrenheit, and is likely tidally locked, meaning that it has a permanent day and night side, presenting the same face to its star, much like our moon is locked to the Earth. Because of its scorching temperatures, GJ 1132b most likely cannot retain liquid water on its surface, making it uninhabitable for life as we know it. However, scientists say it is cool enough to host a substantial atmosphere. The planet is also close enough to Earth that scientists may soon be able to find out much more about its characteristics, from the composition of its atmosphere to the pattern of its winds—and even the color of its sunsets. "If we find this pretty hot planet has managed to hang onto its atmosphere over the billions of years it's been around, that bodes well for the long-term goal of studying cooler planets that could have life," says Zachory Berta-Thompson, a postdoc in MIT's Kavli Institute for Astrophysics and Space Research. "We finally have a target to point our telescopes at, and [can] dig much deeper into the workings of a rocky exoplanet, and what makes it tick." Berta-Thompson and his colleagues discovered the planet using the MEarth-South Observatory, a Harvard University-led array of eight 40-centimeter-wide robotic telescopes located in the mountains of Chile. The array monitors small, nearby stars called M dwarfs, which are scattered all over the night sky. Scientists have determined that these kinds of stars are frequently orbited by planets, but haven't yet found Earth-sized exoplanets that are close enough to study in depth. Since early 2014, the telescope array has been gathering data almost every night, taking measurements of starlight every 25 minutes in search of telltale dips in brightness that may indicate a planet passing in front of a star. On May 10, one telescope picked up a faint dip from GJ 1132, a star located 12 parsecs, or 39 light-years, from Earth. "Our galaxy spans about 100,000 light-years," Berta-Thompson says. "So this is definitely a very nearby solar neighborhood star." The robotic telescope immediately started observing GJ1132 at much faster 45-second intervals to confirm the measurement—a very slight dip of about 0.3 percent of the starlight. The researchers later pointed other telescopes in Chile at the star, and found that indeed, GJ 1132's brightness dimmed by 0.3 percent every 1.6 days—a signal that a planet was regularly passing in front of the star. "We didn't know the planet's period from one single event, but when we phased many of them together, this signal popped out," Berta-Thompson says. Based on the amount of starlight the planet blocks, and the radius of the star, scientists calculated that planet GJ 1132b is about 1.2 times the size of Earth. From measuring the wobble of its host star, they estimate the planet's mass to be about 1.6 times that of Earth. Given its size and mass, they could determine its density—and they believe it to be rocky, like Earth. However, size and composition are where the comparisons to our planet end. By calculating the size of and proximity to its star, the group came up with an estimate of the planet's average temperature: a scorching 500 kelvins, or 440 F. "The temperature of the planet is about as hot as your oven will go, so it's like burnt-cookie hot," Berta-Thompson says. "It's too hot to be habitable—there's no way there's liquid water on the surface. But it is a lot cooler than the other rocky planets that we know of." That's good in terms of scientific study: Most rocky exoplanets that have been discovered so far are essentially fireballs, with surface temperatures in the thousands of degrees—far too hot to hold onto any kind of atmosphere. "This planet is cool enough that it can retain an atmosphere," Berta-Thompson says. "So we think this planet probably still has something of a substantial atmosphere, in its current state." Berta-Thompson hopes that astronomers will use the James Webb Space Telescope (JWST), the much larger successor to the Hubble Space Telescope that is launching in 2018, to identify the color and the chemical makeup of the planet's atmosphere, along with the pattern of its winds. "We think it's the first opportunity we have to point our telescopes at a rocky exoplanet and get that kind of detail, to be able to measure the color of its sunset, or the speed of its winds, and really learn how rocky planets work out there in the universe," Berta-Thompson says. "Those will be exciting observations to make." The MIT-led NASA Transiting Exoplanet Survey Satellite (TESS) will search the entire sky for nearby planets, and may find many more that would serve as good targets for JWST. "Of the billions of star systems in the Milky Way galaxy, about 500 are closer than GJ1132," Berta-Thompson says. "TESS will find planets around some of these stars, and those planets will be valuable comparisons for understanding GJ1132b and rocky planets in general." Explore further: The search for habitable worlds, from sub-Neptunes to super-Earths
Afshordi N.,Perimeter Institute for Theoretical Physics |
Afshordi N.,University of Waterloo |
Mohayaee R.,CNRS Paris Institute of Astrophysics |
Bertschinger E.,Kavli Institute for Astrophysics and Space Research
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010
We develop a theoretical framework for describing the hierarchical structure of the phase space of cold dark matter haloes, due to gravitationally bound substructures. Because it includes the full hierarchy of the cold dark matter initial conditions and is hence complementary to the halo model, the stable clustering hypothesis is applied for the first time here to the small-scale phase-space structure. As an application, we show that the particle dark matter annihilation signal could be up to 2 orders of magnitude larger than that of the smooth halo within the Galactic virial radius. The local boost is inversely proportional to the smooth halo density, and thus is O(1) within the solar radius, which could translate into interesting signatures for dark matter direct detection experiments: The temporal correlation of dark matter detection can change by a factor of 2 in the span of 10 years, while there will be significant correlations in the velocity space of dark matter particles. This can introduce O(1) uncertainty in the direction of local dark matter wind, which was believed to be a benchmark of directional dark matter searches or the annual modulation signal. © 2010 The American Physical Society.
Dark Energy Survey image of the region surrounding the faint dwarf galaxy Reticulum II. The nine brightest known stars in the galaxy are marked with red circles. Spectra showing the unique chemical content of three stars are shown. Credit: Alex Ji. Background image: Fermilab/Dark Energy Survey Reticulum II is an ancient and faint dwarf galaxy discovered in images taken as part of the Dark Energy Survey. It orbits the Milky Way galaxy about 100,000 light years away from us. Though the galaxy looks unassuming at first, the chemical content of its stars may hold the key to unlocking a 60-year-old mystery about the cosmic origin of the heaviest elements in the periodic table. Today in the journal Nature, a team of astronomers at MIT's Kavli Institute for Astrophysics and Space Research and the Observatories of the Carnegie Institution of Washington report on observations of this unique galaxy using the Magellan telescopes at the Las Campanas Observatory in Chile's Atacama Desert. Lead author and MIT physics graduate student Alex Ji explains more. Q: How are the heaviest elements in the periodic table created in the cosmos? A: Carl Sagan popularized the notion that we are all made of star stuff. He could say so with confidence because we actually know where nearly every element in the periodic table is made in the universe. But there's a hole in our understanding. The heaviest elements are made in what is called the "rapid neutron-capture process," or "r-process" for short, in which heavy elements are quickly built up from lighter seed nuclei. Gold, platinum, and uranium are r-process elements, as are more exotic elements like europium, neodymium, and gadolinium. The nuclear physics of the r-process was mostly worked out by 1957, but for almost 60 years astronomers have debated about the astrophysical site that could provide the extreme conditions for the r-process to occur. Synthesizing the r-process elements requires environments with a very large number of neutrons. The two best candidate sites are supernovae and merging neutron stars. Supernovae are the explosions that mark the end of a massive star's life. They often leave behind a remnant called a neutron star. During the formation of a neutron star, a large amount of neutrons is released. If two of these neutron stars happen to be orbiting each other, they will eventually merge to form one giant neutron star. During that explosion neutrons are released and r-process elements can form. Q: How does this dwarf galaxy help us understand the site of the r-process? A: Reticulum II is not the first ancient dwarf galaxy to have its chemical content examined; it's actually the 10th. But its chemical composition differs completely from those other galaxies. The stars in those first nine galaxies have unusually low amounts of r-process elements. Reticulum II, on the other hand, is chock-full of r-process elements. Its stars display some of the highest r-process enhancements we have ever seen. It's almost literally a gold mine. What this means is that a single rare event produced a rather large amount of this r-process material. All those elements were then incorporated into the surrounding gas and from there into the next generations of stars. It is those stars that we can still observe today. The single, prolific r-process event in this galaxy implies that a neutron star merger could have produced these elements in the early universe. A normal supernova would have produced less, and the observed enhancement could not have been as high, though it's also hypothesized that rare, magnetically-driven supernovae might be able to produce much more r-process material. Interestingly, there is indirect evidence that neutron star mergers do also synthesize r-process elements in the universe today. So it looks like neutron star mergers could be the primary r-process sites throughout cosmic time. It's amazing to think that Reticulum II preserved a signature of that extraordinary event for more than 12 billion years, just waiting for us to dig it up. Q: What was it like to be at the telescope and realize what you had found? A: Based on studying the other ultra-faint galaxies, I had expected to find stars with essentially none of these r-process elements and to further establish that these types of dwarf galaxies are devoid in these elements. So we had a plan to get some really good, low upper limits on the r-process content to push this issue. When we realized the stars in this galaxy were the complete opposite, and instead full of r-process elements, I was certain I had screwed something up. From the telescope in Chile I called my advisor Anna Frebel in Cambridge [Mass.] in the middle of the night to urgently talk about what was going on. Telescope time is precious and expensive after all and shouldn't be wasted. During the hour-long discussions that followed, I kept observing more stars while carrying out preliminary analyses of the data at hand to ensure that this was a real signal. At the observatory, astronomers work all night and sleep during the day. But after seeing the r-process elements in the first few stars, I couldn't sleep anymore; all I could do was stare out the window and hope the incoming clouds would go away again and the wind would die down. We were very lucky that it ended up being clear most of the four nights we had available. My last night there, the weather forecast, as translated from Spanish by Google, read "rain and wind." So I prepared myself to get no data that night. But it turned out Google had translated the word "despejado" incorrectly and in fact it was supposed to be "clear and wind." An important translation to get right, especially for astronomers! More information: Alexander P. Ji et al. R-process enrichment from a single event in an ancient dwarf galaxy, Nature (2016). DOI: 10.1038/nature17425
News Article | November 12, 2015
Astronomers say a newly discovered planet almost next door to us — just 39 light-years away — is the closest rocky exoplanet like Earth ever found. It's not like Earth in one respect, though: the atmosphere in its coolest parts is a sizzling 450 to 500 degrees Fahrenheit, making it more like our solar system neighbor Venus than our own world, scientists say. Still, the planet's proximity to us and its resemblance to Earth in at least its diameter and mass make it "arguably the most important planet ever found outside the solar system," Drake Demming of the University of Maryland wrote in a commentary accompanying the published study on the discovery. Just 16 percent larger than Earth, the planet GJ 1132b orbits a dim star just one-fifth the size of our sun. It's close to its parent star, orbiting at just 1.4 million miles away. For comparison, Mercury in our solar system orbits our sun at 36 million miles. At just 39 light-years away, its parent star, Gliese 1132, is a close neighbor in the Milky Way. "Our galaxy spans about 100,000 light-years," said Zachory Berta-Thompson, a postdoctoral researcher at MIT's Kavli Institute for Astrophysics and Space Research. "So this is definitely a very nearby solar neighborhood star." The planet GJ 1132b is probably tidally locked in its orbit, which means it always presents the same face to its star, creating a permanent and unchanging day and night side. Because of its sizzling temperature, it's unlikely to retain liquid water on its surface, making it almost certainly uninhabitable, the scientists say. Still, it's cool enough to have retained a significant atmosphere, they point out, which makes it an interesting subject for study. "If we find this pretty hot planet has managed to hang onto its atmosphere over the billions of years it's been around, that bodes well for the long-term goal of studying cooler planets that could have life," explained Berta-Thompson. Its nearness provides an unprecedented opportunity to make observations, since most Earth-sized planets discovered so far are thousands of light-years distant from us. "We finally have a target to point our telescopes at, and [can] dig much deeper into the workings of a rocky exoplanet, and what makes it tick," Berta-Thompson said. While it may be more like Venus than the Earth, it will allow scientists to test theories about rocky planets, how they form, how they end up in their particular orbits and what physical process takes place on their surfaces. "Our ultimate goal is to find a twin Earth, but along the way we've found a twin Venus," said astronomer David Charbonneau of the Harvard-Smithsonian Center for Astrophysics. "We suspect it will have a Venus-like atmosphere too, and if it does we can't wait to get a whiff."