More than 1,200 new planets confirmed using new technique for verifying Kepler data

The researchers used an automated software developed at Princeton known as Vespa that allows scientists to efficiently determine if a Kepler signal is caused by a planet. Vespa computes the chances that a Kepler signal actually came from a certain type of planet. Automated software such as Vespa is necessary because of the sheer amount of Kepler data and the similarity that some planetary signals — especially those of larger planets — have to other objects such as stars that orbit each other. The graph above shows the type of planets newly verified by Vespa (orange) compared to the number of those planets previously confirmed (blue). Vespa more likely verified smaller planets because of their prevalence and unambiguous signal; signals thought to come from less common Jupiter-sized planets were more likely to actually emanate from stars. (Graph courtesy of NASA)

The researchers used an automated software developed at Princeton known as Vespa that allows scientists to efficiently determine if a Kepler signal is caused by a planet. Vespa computes the chances that a Kepler signal actually came from a certain type of planet. Automated software such as Vespa is necessary because of the sheer amount of Kepler data and the similarity that some planetary signals — especially those of larger planets — have to other objects such as stars that orbit each other. The graph above shows the type of planets newly verified by Vespa (orange) compared to the number of those planets previously confirmed (blue). Vespa more likely verified smaller planets because of their prevalence and unambiguous signal; signals thought to come from less common Jupiter-sized planets were more likely to actually emanate from stars. (Graph courtesy of NASA)

Scientists from Princeton University and NASA have confirmed that 1,284 objects observed outside Earth’s solar system by NASA’s Kepler spacecraft are indeed planets. Reported in The Astrophysical Journal on May 10, it is the largest single announcement of new planets to date and more than doubles the number of confirmed planets discovered by Kepler so far to more than 2,300.

The researchers’ discovery hinges on a technique developed at Princeton that allows scientists to efficiently analyze thousands of signals Kepler has identified to determine which are most likely to be caused by planets and which are caused by non-planetary objects such as stars. This automated technique — implemented in a publicly available custom software package called Vespa — computes the chances that the signal is in fact caused by a planet.

The researchers used Vespa to compute the reliability values for over 7,000 signals identified in the latest Kepler catalog, and verified the 1,284 planets with 99 percent certainty. They also independently verified 651 additional planet signals that had already been confirmed as planets by other methods. In addition, the researchers identified 428 candidates as likely “false positives,” or signals generated by something other than a planet.

Timothy Morton, lead author of the study and a Princeton associate research scholar of astrophysical sciences, developed Vespa because the vast amount of data Kepler has gathered since its 2009 launch has made the traditional method of confirming planets by direct ground-based follow-up observation untenable, he said. Follow-up observations of Kepler data had confirmed a little more than a thousand planets prior to the Princeton-NASA announcement.

“Vespa is a culmination of a change in attitude about how we deal with these large-data surveys,” Morton said. “This new problem Kepler created is that we now have thousands of new planet candidates. Astronomers knew we couldn’t follow up all of these in the traditional way, but there was nothing to replace it. This result now puts a number on exactly how likely it is that each detected object is a planet.”

Kepler, which ended data collection for its primary mission in 2013, operated by precisely measuring the brightness of many stars simultaneously. The satellite looked for stars that exhibited subtle and regular dimming, which indicates that an orbiting planet is passing in front of, or transiting, that star.

However, some scenarios can mimic the signature of a transiting planet, such as two stars that orbit each other, and provide a false positive signal. Distinguishing between true planets and false positives is one of the central challenges for any transiting planet survey, Morton said.

Joshua Winn, an associate professor of physics at the Massachusetts Institute of Technology and former member of the Kepler team, said that efficient methods to confirm planets will become more crucial as NASA plans and launches more space telescopes, such as the Transiting Exoplanet Survey Satellite (TESS), which is expected to find tens of thousands of exoplanets.

The one-by-one confirmation process of Kepler data has been an obstacle to scientists making as many discoveries from the data as they might have, said Winn, who is the deputy science director of TESS.

“The data rate from [TESS] will be even higher than that of Kepler, making it even more important to have trustworthy algorithms to calculate the odds that a given signal really arises from a planet as opposed to an ‘imposter,'” said Winn, who is familiar with the Vespa research but had no role in it.

“Morton and his colleagues have provided an automated and effective means of assessing the probability that a given signal arises from a planet,” he said. “It’s exactly what the exoplanet community needs to tell the real gold apart from the counterfeits.”

The Vespa technique works by comparing the details of a transiting planet signal — specifically its duration, depth and shape — against simulated planetary and false positive signals to indicate the type of signal the candidate most likely is. At the same time, Vespa factors in the projected distribution and frequency of star types in the galaxy from which the signal originated to determine the chances that a planet with the characteristics being analyzed would exist.

Vespa was designed to supplement the internal vetting of Kepler data, Morton said. A signal from the raw Kepler data is designated a planet candidate after a series of tests within the data-processing pipeline that are intended to weed out as many imposters as possible. These procedures rule out a large portion of false positives, Morton said. In fact, more than 3,000 of the signals from the latest catalog were already identified as false positives well before Morton applied the recent Vespa analysis. Vespa is more likely to validate an internal ruling that a signal came from a small planet because of their frequency and unambiguous signal, Morton said.

“If you have something that passes all those tests, then it’s likely to be a planet,” Morton said. “We know small planets are common, so if Kepler sees a small-looking planet candidate and it passes the strict internal vetting, it’s more likely to be a planet than a false positive because it’s hard to mimic that signal with anything else.”

On the other hand, if a planet candidate has the characteristics of a Jupiter-sized planet, Vespa is less likely to verify it as a planet. The signal could very well emanate from something else because of the relative rarity of Jupiter-sized planets, Morton said. A number of planet candidates are three to four times larger than Jupiter, which means that Kepler most likely detected double-star systems in which one star was passing in front of the other.

“It’s easier to mimic something the size of Jupiter, and we know Jupiter-sized planets are less common,” Morton said. “So the likelihood of a Jupiter-sized candidate actually being a planet that large is typically relatively low.”

Learn more: More than 1,200 new planets confirmed using new technique for verifying Kepler data

 

 

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Rethinking Interstellar Travel and Interstellar Spacecraft to Get There From Here

Laser propulsion (Q. Zhang)

Since the beginning of spaceflight, humans have accomplished wonderful feats of exploration and showcased their drive to understand the universe.

Yet, in those 60 years, only one spacecraft, Voyager 1 (launched in 1977) has left the solar system. As remarkable as this is, humans will never reach even the nearest stars with out current propulsion technology. Instead, radically new strategies involving the technology already available must be used.

We propose a roadmap to a program that will lead to sending relativistic probes to the nearest stars.

To do so requires a fundamental change in our thinking of both propulsion and our definition of what a spacecraft is. In addition to larger spacecrafts capable of human transportation, we consider “wafer sats”, wafer-scale systems weighing no more than a gram. The wafer sats would include integrated optical communications, optical systems, and sensors. These crafts, combined with directed energy propulsion, could be capable of speeds greater than 0.25 c.

This program has applications for planetary defense, SETI and Kepler missions.

Example of Spacecraft Propelled by Laser
Consider a 10 g payload attached to a 2 m diameter sail (left) and a 1 g payload attached to a 0.7 m sail. The bare spacecraft mass is equal to the sail mass. In this example of a small system the laser array propelling the craft has an optical power of 272 kW and is 20 m diameter. The laser and craft both start in low Earth orbit. The array remains in low Earth orbit while the craft is slowly propelled away, spiraling outward from the Earth. The following simulation shows the trajectory of the craft over the first week of propulsion while still in Earth orbit. The craft will ultimately leave the Earth orbit completely in both cases. This is an optimized solution.
Orbital Simulation of Laser Propelling a Spacecraft
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The richness of the interstellar medium from the sun to the nearest stars (Keck Institute for Space Studies)

 

 

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NASA Kepler Results Usher in a New Era of Astronomy

candidate-sizes-histo_2013-wide_0

From the first three years of Kepler data, more than 3,500 potential worlds have emerged. Since the last update in January, the number of planet candidates identified by Kepler increased by 29 percent and now totals 3,538. The largest increase of 78 percent was found in the Earth-sized category. Image Credit: NASA

New Kepler data analysis and research also show that most stars in our galaxy have at least one planet

Scientists from around the world are gathered this week at NASA’s Ames Research Center in Moffett Field, Calif., for the second Kepler Science Conference, where they will discuss the latest findings resulting from the analysis of Kepler Space Telescope data.

Included in these findings is the discovery of 833 new candidate planets, which will be announced today by the Kepler team. Ten of these candidates are less than twice the size of Earth and orbit in their sun’s habitable zone, which is defined as the range of distance from a star where the surface temperature of an orbiting planet may be suitable for liquid water.

At this conference two years ago, the Kepler team announced its first confirmed habitable zone planet, Kepler-22b. Since then, four more habitable zone candidates have been confirmed, including two in a single system.

New Kepler data analysis and research also show that most stars in our galaxy have at least one planet. This suggests that the majority of stars in the night sky may be home to planetary systems, perhaps some like our solar system.

“The impact of the Kepler mission results on exoplanet research and stellar astrophysics is illustrated by the attendance of nearly 400 scientists from 30 different countries at the Kepler Science Conference,” said William Borucki, Kepler science principal investigator at Ames. “We gather to celebrate and expand our collective success at the opening of a new era of astronomy.”

From the first three years of Kepler data, more than 3,500 potential worlds have emerged. Since the last update in January, the number of planet candidates identified by Kepler increased by 29 percent and now totals 3,538. Analysis led by Jason Rowe, research scientist at the SETI Institute in Mountain View, Calif., determined that the largest increase of 78 percent was found in the category of Earth-sized planets, based on observations conducted from May 2009 to March 2012. Rowe’s findings support the observed trend that smaller planets are more common.

An independent statistical analysis of nearly all four years of Kepler data suggests that one in five stars like the sun is home to a planet up to twice the size of Earth, orbiting in a temperate environment. A research team led by Erik Petigura, doctoral candidate at University of California, Berkeley, used publicly accessible data from Kepler to derive this result.

Kepler data also fueled another field of astronomy dubbed asteroseismology — the study of the interior of stars. Scientists examine sound waves generated by the boiling motion beneath the surface of the star. They probe the interior structure of a star just as geologists use seismic waves generated by earthquakes to probe the interior structure of Earth.

“Stars are the building blocks of the galaxy, driving its evolution and providing safe harbors for planets. To study the stars, one truly explores the galaxy and our place within it,” said William Chaplin, professor for astrophysics at the University of Birmingham in the United Kingdom. “Kepler has revolutionized asteroseismology by giving us observations of unprecedented quality, duration and continuity for thousands of stars. These are data we could only have dreamt of a few years ago.”

Kepler’s mission is to determine what percentage of stars like the sun harbor small planets the approximate size and temperature of Earth. For four years, the space telescope simultaneously and continuously monitors the brightness of more than 150,000 stars, recording a measurement every 30 minutes. More than a year of the collected data remains to be fully reviewed and analyzed.

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Closer to encounter

As the latest rover arrives on Mars to assess its hospitality, astronomers are learning more about possibly habitable worlds beyond the solar system.

IF MARTIANS exist, then any in the vicinity of Gale Crater on the Martian equator are in for a treat. On August 6th, assuming its complex landing system works, a plutonium-powered rover the size of a car will be set down on the surface. This is NASA’s Mars Science Laboratory (MSL), the biggest and most sophisticated rover sent anywhere in the solar system. It is going to Mars for several reasons, but the most publicised part of its mission is to continue the hunt for signs of extra-terrestrial life.

Thirty-six years after the arrival of America’s Viking landers, which were designed to see if the Martian regolith hosted alien microbes, astronomers are still unsure if the planet has ever been habitable. The consensus is that Viking found nothing. And Mars is certainly an inhospitable place; temperatures can fall below -100°C, far below those in Antarctica, and an extremely thin atmosphere does little to dampen the solar radiation that bombards a surface as dry as any earthly desert.

There are reasons to believe that the Red Planet was not always as barren. Data from previous missions left planetary scientists convinced that, in its distant past, Mars was much wetter than it is today. Water is widely thought to be vital for life, thanks to its properties as a solvent. A thicker atmosphere, less eroded by the solar wind, might have allowed large bodies of water to persist for long periods on or near the surface.

That may have been enough for life to get started. Geology suggests that primitive life, at least, gets going fairly easily. The first traces of living organisms on Earth date back 3.8 billion years, not long after the planet had cooled sufficiently for liquid water to condense, and soon after the Late Heavy Bombardment, a rain of meteorites that lasted hundreds of millions of years, had begun to slacken off. Some scientists—inspired by the discovery in the 1980s and 1990s of “extremophiles”, bacteria which will happily tolerate blistering heat, crushing pressure, sizzling radiation and other insults on Earth—hold out hope that a few hardy Martians may cling on today, perhaps beneath the surface.

If they do, not even Curiosity, as the rover is called, is likely to find them. It carries high-tech instruments, including a laser for vaporising chunks of rock (the better to analyse their chemical composition) and a drill for probing below the surface to explore the chemical record and hunt for any organic molecules that may have survived. It will also examine the atmosphere, paying particular attention to methane levels, which some scientists think may be high enough to suggest metabolic activity of some sort. If it turns up persuasive evidence that Mars could once have supported life, it would be a big discovery and would raise hopes for future missions designed explicitly to look for living cells, such as Europe’s ExoMars rover. Even if Curiosity finds nothing, there are other possibilities within the solar system: Saturn’s moon Enceladus, for instance, seems to have an underground ocean rich in organic compounds.

But these days the search for habitable worlds is not confined to the solar system. On July 28th NASA released the latest batch of data from its Kepler space telescope. This is designed to look for “exoplanets” that orbit other stars. Their existence is given away by a tiny drop in brightness caused when a planet transits in front of its parent star, as seen from Earth. Launched in 2009, Kepler’s mission is to stare at around 150,000 stars in the constellation of Cygnus, tallying all the planets it can see to discern just how common Earth-sized, temperate, habitable planets may be.

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Planets Galore

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Not that long ago, the possibility of finding planets outside our solar system was merely theoretical.

In 1995, astronomers began to be able to detect Jupiter-sized “exoplanets” by their gravitational effect on the stars they orbit. And with the launch of the Kepler satellite in March 2009 and the release last week of the data it has so far gathered, astronomy has crossed a major threshold. The Kepler has discovered 1,235 potential planets.

What makes this so striking is the satellite’s instruments always point at the same tiny arc of the Milky Way near the constellation called the Northern Cross — only one four-hundredth of the sky. The Kepler team leader, William Borucki, at the Ames Research Center in Northern California, says that if Kepler could see the whole sky, it would have found some 400,000 planets.

The satellite detects possible planets by measuring the light of 156,000 stars in its field of view and looking for slight dips in brightness when a planet crosses in front of a star. All of these planets will have to be validated using telescopes. That will take years, given the limited number of astronomers and powerful telescopes on this planet.

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