NASA’s Exoplanet Exploration
NASA’s Webb Observatory Requires More Time for Testing and Evaluation; New Launch Window Under Review
NASA Release by Jen Rae Wang / Steve Cole
Written by Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
October 21, 2016
This artist’s concept depicts ”heartbeat stars,” which have been detected by NASA’s Kepler Space Telescope and others. Image credit: NASA/JPL-Caltech
Matters of the heart can be puzzling and mysterious – so too with unusual astronomical objects called heartbeat stars.
Heartbeat stars, discovered in large numbers by NASA’s Kepler space telescope, are binary stars (systems of two stars orbiting each other) that got their name because if you were to map out their brightness over time, the result would look like an electrocardiogram, a graph of the electrical activity of the heart. Scientists are interested in them because they are binary systems in elongated elliptical orbits. This makes them natural laboratories for studying the gravitational effects of stars on each other.
In a heartbeat star system, the distance between the two stars varies drastically as they orbit each other. Heartbeat stars can get as close as a few stellar radii to each other, and as far as 10 times that distance during the course of one orbit.
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Astronomers have discovered what appears to be a tiny star with a giant, cloudy storm, using data from NASA’s Spitzer and Kepler space telescopes. The dark storm is akin to Jupiter’s Great Red Spot: a persistent, raging storm larger than Earth.
“The star is the size of Jupiter, and its storm is the size of Jupiter’s Great Red Spot,” said John Gizis of the University of Delaware, Newark. “We know this newfound storm has lasted at least two years, and probably longer.” Gizis is the lead author of a new study appearing in The Astrophysical Journal.
While planets have been known to have cloudy storms, this is the best evidence yet for a star that has one. The star, referred to as W1906+40, belongs to a thermally cool class of objects called L-dwarfs. Some L-dwarfs are considered stars because they fuse atoms and generate light, as our sun does, while others, called brown dwarfs, are known as “failed stars” for their lack of atomic fusion.
The L-dwarf in the study, W1906+40, is thought to be a star based on estimates of its age (the older the L-dwarf, the more likely it is a star). Its temperature is about 3,500 degrees Fahrenheit (2,200 Kelvin). That may sound scorching hot, but as far as stars go, it is relatively cool. Cool enough, in fact, for clouds to form in its atmosphere.
“The L-dwarf’s clouds are made of tiny minerals,” said Gizis.
Spitzer has observed other cloudy brown dwarfs before, finding evidence for short-lived storms lasting hours and perhaps days.
In the new study, the astronomers were able to study changes in the atmosphere of W1906+40 for two years. The L-dwarf had initially been discovered by NASA’s Wide-field Infrared Survey Explorer in 2011. Later, Gizis and his team realized that this object happened to be located in the same area of the sky where NASA’s Kepler mission had been staring at stars for years to hunt for planets.
Kepler identifies planets by looking for dips in starlight as planets pass in front of their stars. In this case, astronomers knew observed dips in starlight weren’t coming from planets, but they thought they might be looking at a star spot — which, like our sun’s “sunspots,” are a result of concentrated magnetic fields. Star spots would also cause dips in starlight as they rotate around the star.
Follow-up observations with Spitzer, which detects infrared light, revealed that the dark patch was not a magnetic star spot but a colossal, cloudy storm with a diameter that could hold three Earths. The storm rotates around the star about every 9 hours. Spitzer’s infrared measurements at two infrared wavelengths probed different layers of the atmosphere and, together with the Kepler visible-light data, helped reveal the presence of the storm.
While this storm looks different when viewed at various wavelengths, astronomers say that if we could somehow travel there in a starship, it would look like a dark mark near the polar top of the star.
The researchers plan to look for other stormy stars and brown dwarfs using Spitzer and Kepler in the future.
“We don’t know if this kind of star storm is unique or common, and we don’t why it persists for so long,” said Gizis.
NASA’s Ames Research Center in Moffett Field, California, manages the Kepler and K2 missions for NASA’s Science Mission Directorate. JPL managed Kepler mission development. Ball Aerospace & Technologies Corp. operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.
JPL manages the Spitzer Space Telescope mission for NASA. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech.
Caltech manages JPL for NASA.
The Sagan Fellowship program, named after the late Carl Sagan, supports talented young scientists in their mission to explore the unknown. Following the path laid out by Sagan, these bright fellows will continue to tread the path, make their own discoveries and inspire future Sagan fellows. Image credit: NASA/Cosmos Studies
“The Sagan Fellowships attract the best and brightest early career researchers in the rapidly developing field of exoplanets. They are pushing the boundaries of finding and characterizing the most Earth-like around the coolest, nearest stars,” said Charles Beichman, executive director of the NASA Exoplanet Science Institute at the California Institute of Technology in Pasadena. “Their research will make advances in exoplanet theory and instrumentation, and take full advantage of NASA missions.”
The 2015 Sagan Fellows are:
- Courtney Dressing, who will work at the California Institute of Technology in Pasadena on “Characterizing Small Planets Orbiting Small Stars.” Dressing will use data from NASA’s Kepler space telescope and its follow-on mission, K2, to distinguish false positive planet candidates and to characterize red dwarfs hosting small planets. She will also measure the mass of small planets to further characterize their compositional properties and investigate the link between stellar hosts and planetary properties.
- Daniel Foreman-Mackey, who will work at the University of Washington in Seattle on “Flexible and Robust Inference of the Exoplanet Population.” Foreman-Mackey will use statistical methods to examine the large catalog of exoplanet discoveries, studying their distribution as a function of their physical parameters. He plans to derive a common framework for robust population inference and to apply this method to existing and forthcoming catalogs of exoplanet data.
- Jonathan Gagne, who will work at the Carnegie Institute for Science in Washington on “Locating the Young, Isolated Planetary-Mass Objects in the Solar Neighborhood.” Gagne will use ground-based observations to explore the connection between the atmospheres of brown dwarfs and those of giant exoplanets. This will constrain the initial mass function down to a few times the mass of Jupiter, hence testing the recent prediction that the spatial density of isolated Jupiter-mass objects is twice as large as that of stars.
- Paul Robertson, who will work at Pennsylvania State University in State College on “Spotting Blue Planets Around Spotted Red Stars: Removing Stellar Activity from Radial Velocities of M Dwarf Stars.” Robertson plans to develop a generalized method for disentangling stellar activity from radial velocity (RV) measurements of M stars in near-infrared wavelengths. He will develop a multi-dimensional modeling package that simultaneously models planet signals and activity-RV correlations, rather than separating analyses of the two. This will lead to robust detections of low-mass planets in the habitable zone.
- Ty Robinson, who will work at the University of California in Santa Cruzon “Bridging the Theory Gap: Developing a Novel Cloud Model for Exoplanets.” Robinson is interested in understanding cloud dynamics which are key to characterizing and modeling exoplanets. Clouds strongly influence many exoplanet observations, and Robinson will work toward developing new and efficient cloud models that lead to better interpretation of exoplanet observations.
- Leslie Rogers, who will work at the University of California in Berkeley on “Searching for Water in Distant Worlds.” Rogers will use three approaches, atmospheric transmission spectra, exoplanet radio aurora emissions, and the accumulating statistical ensemble of planet mass-radius, to constrain the bulk water content of distant exoplanets. These data will be used to evaluate planet formation theories for the abundance of Neptune-sized exoplanets.