Tag Archives: astrophysics

European satellite could discover thousands of planets in Earth’s galaxy (arXiv)

By Morgan Kelly, Office of Communications

Celestial Sphere

Princeton University and Lund University researchers project that the recently launched European satellite Gaia could discover tens of thousands of planets during its five-year mission. In this image, the colored portions indicate the number of observations Gaia would make of a particular part of the sky during its mission; the scale at the bottom indicates the number of observations from zero (purple) to 200 (red). The total number of observations of any part of the sky ranges from about 60 at low ecliptic latitudes to about 80 at high ecliptic latitudes, with a maximum of about 150-200 at intermediate latitudes. From these many different observations of each star, the highly accurate Gaia measurements will reveal the tiny star motion, or “wobble,” that results from any orbiting planet. (Image by Lennart Lindegren, Lund University)

A recently launched European satellite could reveal tens of thousands of new planets within the next few years, and provide scientists with a far better understanding of the number, variety and distribution of planets in our galaxy, according to research published today.

Researchers from Princeton University and Lund University in Sweden calculated that the observational satellite Gaia could detect as many as 21,000 exoplanets, or planets outside of Earth’s solar system, during its five-year mission. If extended to 10 years, Gaia could detect as many as 70,000 exoplanets, the researchers report. The researchers’ assessment is accepted in the Astrophysical Journal and was published Nov. 6 in advance-of-print on arXiv, a preprint database run by Cornell University.

Exoplanets will be an important “by-product” of Gaia’s mission, explained first author Michael Perryman, who made the assessment while serving as Princeton’s Bohdan Paczyński Visiting Fellow in the Department of Astrophysical Sciences. Built and operated by the European Space Agency (ESA) and launched in December 2013, Gaia will capture the motion, physical characteristics and distance from Earth — and one another — of roughly 1 billion objects, mostly stars, in the Milky Way galaxy with unprecedented precision. The presence of an exoplanet will be determined by how its star “wobbles” as a result of the planet’s orbit around it.

More important than the numbers of predicted discoveries are the kinds of planets that the researchers expect Gaia to detect, many of which — such as planets with multi-year orbits that pass directly, or transit, in front of their star as seen from Earth — are currently difficult to find, Perryman said. The satellite’s instruments could reveal objects that are considered rare in the Milky Way, such as an estimated 25 to 50 Jupiter-sized planets that orbit faint, low-mass stars known as red dwarfs. Unique planets and systems — such as planets that orbit in the opposite direction of their companions — can inspire years of research, he said.

Transit Distances

One of the main objectives of the Gaia mission is to establish the currently uncertain distance from Earth to various stars using high-precision triangulation, which would allow a much better understanding of the properties of the stars and the planets orbiting them. Of the 1,163 confirmed transiting planets, which pass directly in front of their stars as seen from Earth, there are 644 distinct host stars; less than 200 have accurately known distances from Earth. This image shows the distances from Earth (center) to the stars (black dots) of transiting exoplanets. The inner dashed circle has a radius of 100 parsecs (about 326 light years) with the middle and outer circles corresponding to 500 parsecs (1,630 light years) and 1,000 parsecs (3,260 light years), respectively. The cluster of points to the lower right represents the transiting planets discovered by NASA’s Kepler satellite. For each star, the straight lines extending from the circle indicate the current uncertainty of its distance from Earth. (Image by Michael Perryman)

“It’s not just about the numbers. Each of these planets will be conveying some very specific details, and many will be highly interesting in their own way,” Perryman said. “If you look at the planets that have been discovered until now, they occupy very specific regions of discovery space. Gaia will not only discover a whole list of planets, but in an area that has not been thoroughly explored so far.”

Ultimately, a comprehensive census allows scientists to more accurately determine how many planets and planetary systems exist, the detailed properties of those planets, and how they are positioned throughout the galaxy, Perryman said.

Perryman worked with Joel Hartman, an associate research scholar in Princeton’s astrophysical sciences department, Gáspár Bakos, an associate professor of astrophysical sciences, and Lennart Lindegren, a professor of astronomy at Lund University. Gaia is based on a satellite proposal led by Lindegren and Perryman that was submitted to the ESA in 1993.

Research on exoplanets has increased dramatically in the 15 years since Gaia was accepted by the ESA in 2000. The new estimate is based on a highly detailed model of how stars and planets are positioned in the Milky Way; more accurate details of Gaia’s measurement and data-analysis capabilities; and current estimates of exoplanet distributions, particularly those derived from NASA’s Kepler satellite, which has identified nearly 1,000 confirmed planets and more than 3,000 candidates. Crucial to conducting the assessment is the much-improved knowledge that now exists about distant planets, Perryman said, such as the types of stars that exoplanets orbit.

The first exoplanet was detected in 1995. Nearly 1,900 have since been discovered. Bakos, who focuses much of his research on exoplanets, launched and oversees HATNet (Hungarian-made Automated Telescope Network) and HATSouth, planet-hunting networks of fully automated, small-scale telescopes installed on four continents that scan the sky every night for planets as they transit in front of their parent star. The projects have discovered more than 50 planets since 1999.

“Our assessment will help prepare exoplanet researchers for what to expect from Gaia,” Perryman said. “We’re going to be adding potentially 20,000 new planets in a completely new area of discovery space. It’s anyone’s guess how the field will develop as a result.”

This work was partly supported by the National Science Foundation (grant no. 1108686) and NASA (grant no. NNX13AJ15G).

Read the article.

Michael Perryman, Joel Hartman, Gáspár Bakos and Lennart Lindegren. 2014. Astrometric exoplanet detection with Gaia. Astrophysical Journal. Arti­cle first pub­lished to the arXiv preprint database: Nov. 6, 2014.

 

Rife with hype, exoplanet study needs patience and refinement (PNAS)

By Morgan Kelly, Office of Communications

Exoplanet

Exoplanet transiting in front of its star. Princeton’s Adam Burrows argues against drawing too many conclusions about such distant objects with today’s technologies. Photo credit: ESA/C. Carreau

Imagine someone spent months researching new cities to call home using low-resolution images of unidentified skylines. The pictures were taken from several miles away with a camera intended for portraits, and at sunset. From these fuzzy snapshots, that person claims to know the city’s air quality, the appearance of its buildings, and how often it rains.

This technique is similar to how scientists often characterize the atmosphere — including the presence of water and oxygen — of planets outside of Earth’s solar system, known as exoplanets, according to a review of exoplanet research published in the Proceedings of the National Academy of Sciences.

A planet’s atmosphere is the gateway to its identity, including how it was formed, how it developed and whether it can sustain life, stated Adam Burrows, author of the review and a Princeton University professor of astrophysical sciences.

But the dominant methods for studying exoplanet atmospheres are not intended for objects as distant, dim and complex as planets trillions of miles from Earth, Burrows said. They were instead designed to study much closer or brighter objects, such as planets in Earth’s solar system and stars.

Nonetheless, scientific reports and the popular media brim with excited depictions of Earth-like planets ripe for hosting life and other conclusions that are based on vague and incomplete data, Burrows wrote in the first in a planned series of essays that examine the current and future study of exoplanets. Despite many trumpeted results, few “hard facts” about exoplanet atmospheres have been collected since the first planet was detected in 1992, and most of these data are of “marginal utility.”

The good news is that the past 20 years of study have brought a new generation of exoplanet researchers to the fore that is establishing new techniques, technologies and theories. As with any relatively new field of study, fully understanding exoplanets will require a lot of time, resources and patience, Burrows said.

“Exoplanet research is in a period of productive fermentation that implies we’re doing something new that will indeed mature,” Burrows said. “Our observations just aren’t yet of a quality that is good enough to draw the conclusions we want to draw.

“There’s a lot of hype in this subject, a lot of irrational exuberance. Popular media have characterized our understanding as better than it actually is,” he said. “They’ve been able to generate excitement that creates a positive connection between the astrophysics community and the public at large, but it’s important not to hype conclusions too much at this point.”

The majority of data on exoplanet atmospheres come from low-resolution photometry, which captures the variation in light and radiation an object emits, Burrows reported. That information is used to determine a planet’s orbit and radius, but its clouds, surface, and rotation, among other factors, can easily skew the results. Even newer techniques such as capturing planetary transits — which is when a planet passes in front of its star, and was lauded by Burrows as an unforeseen “game changer” when it comes to discovering new planets — can be thrown off by a thick atmosphere and rocky planet core.

All this means that reliable information about a planet can be scarce, so scientists attempt to wring ambitious details out of a few data points. “We have a few hard-won numbers and not the hundreds of numbers that we need,” Burrows said. “We have in our minds that exoplanets are very complex because this is what we know about the planets in our solar system, but the data are not enough to constrain even a fraction of these conceptions.”

Burrows emphasizes that astronomers need to acknowledge that they will never achieve a comprehensive understanding of exoplanets through the direct-observation, stationary methods inherited from the exploration of Earth’s neighbors. He suggests that exoplanet researchers should acknowledge photometric interpretations as inherently flawed and ambiguous. Instead, the future of exoplanet study should focus on the more difficult but comprehensive method of spectrometry, wherein the physical properties of objects are gauged by the interaction of its surface and elemental features with light wavelengths, or spectra. Spectrometry has been used to determine the age and expansion of the universe.

Existing telescopes and satellites are likewise vestiges of pre-exoplanet observation. Burrows calls for a mix of small, medium and large initiatives that will allow the time and flexibility scientists need to develop tools to detect and analyze exoplanet spectra. He sees this as a challenge in a research environment that often puts quick-payback results over deliberate research and observation. Once scientists obtain high-quality spectral data, however, Burrows predicted, “Many conclusions reached recently about exoplanet atmospheres will be overturned.”

“The way we study planets out of the solar system has to be radically different because we can’t ‘go’ to those planets with satellites or probes,” Burrows said. “It’s much more an observational science. We have to be detectives. We’re trying to find clues and the best clues since the mid-19th century have been in spectra. It’s the only means of understanding the atmosphere of these planets.”

A longtime exoplanet researcher, Burrows predicted the existence of “hot-Jupiter” planets — gas planets similar to Jupiter but orbiting very close to the parent star — in a paper in the journal Nature months before the first such planet, 51 Pegasi b, was discovered in 1995.

Read the abstract.

Citation: Burrows, Adam S. 2014. Spectra as windows into exoplanet atmospheres. Proceedings of the National Academy of Sciences. Article first published online: Jan. 13, 2014. DOI: 10.1073/pnas.1304208111

Shape from sound — new methods to probe the universe (Physical Review Letters)

By Morgan Kelly, Office of Communications

As the universe expands, it is continually subjected to energy shifts, or “quantum fluctuations,” that send out little pulses of “sound” into the fabric of spacetime. In fact, the universe is thought to have sprung from just such an energy shift.

A recent paper in the journal Physical Review Letters reports a new mathematical tool that should allow one to use these sounds to help reveal the shape of the universe. The authors reconsider an old question in spectral geometry that asks, roughly, to what extent can the shape of a thing be known from the sound of its acoustic vibrations? The researchers approached this problem by breaking it down into small workable pieces, according to author Tejal Bhamre, a Princeton University graduate student in the Department of Physics.

To understand the authors’ method, consider a vase. If one taps a vase with a spoon, it will make a sound that is characteristic of its shape. Similarly, the technique Bhamre and her coauthors developed could, in principle, determine the shape of spacetime from the perpetual ringing caused by quantum fluctuations.

The researchers’ technique also provides a unique connection between the two pillars of modern physics — quantum theory and general relativity — by using vibrational wavelengths to define the geometric property that is spacetime.

Bhamre worked with coauthors David Aasen, a physics graduate student at Caltech, and Achim Kempf, a Waterloo University professor of physics of information.

Read the abstract.

David Aasen, Tejal Bhamre and Achim Kempf. 2013. Shape from Sound: Toward New Tools for Quantum Gravity. Physical Review Letters. Article first published online: March 18, 2013. DOI: 10.1103/PhysRevLett.110.121301.

This research was supported by the Natural Sciences and Engineering Research Council of Canada.