TESS Finds Possible New Worlds Using Stellar Eclipses

A gas giant planet looms in the foreground at right, illuminated by a pair of stars, in this artist’s concept of a world in a binary system. NASA’s TESS (Transiting Exoplanet Survey Satellite) has found planets in two binary star systems by looking for stellar dimming as the planets cross in front of one of the stars. Astronomers have now demonstrated a new method of finding planets in these systems by focusing on the timing of the stars’ mutual eclipses.

Credit: NASA's Goddard Space Flight Center/Chris Smith (USRA)

Alt text: Planet orbiting a binary system

Image description: Against a starry sky suffused with an orange glow, a gas giant planet with purple and white clouds appears in its crescent phase at right. Two bright stars illuminate the scene, one large and whitish at left, the other smaller and more orange near the center.

A gas giant planet looms in the foreground at the bottom, illuminated by a pair of stars, in this artist’s concept of a world in a binary system. NASA’s TESS (Transiting Exoplanet Survey Satellite) has found planets in two binary star systems by looking for stellar dimming as the planets cross in front of one of the stars. Astronomers have now demonstrated a new method of finding planets in these systems by focusing on the timing of the stars’ mutual eclipses.

Credit: NASA's Goddard Space Flight Center/Chris Smith (USRA)

Alt text: Planet orbiting a binary system

Image description: Against a starry sky suffused with an orange glow, a gas giant planet with purple and white clouds appears in its crescent phase at bottom. Two bright stars illuminate the scene, one large and whitish at top center, the other smaller and more orange below it.

Explore how observations of stellar eclipses can expand the capabilities of NASA’s TESS, leading to the discovery of new candidate planets it couldn’t otherwise detect.

Credit: NASA’s Goddard Space Flight Center/Francis Reddy

Alt text: Infographic outlining the new discovery method

Image descriptiopn: Four panels of text and illustrations appear on a dark blue background. The title reads “How TESS Finds Planets Using Stellar Eclipses.”

1: The top panel contains three illustrations. At left, in shades of light blue, is a picture of the TESS satellite. In the middle, several images of a planet, attached to a blue arrow indicating motion to the right, appear silhouetted against the disk of an orange star. Labels read “Star” and “Planet’s path.” The text below reads “NASA’s TESS (Transiting Exoplanet Survey Satellite) finds alien worlds by looking for planets that cross in front of their stars. This passage is called a transit.” At right, a fuzzy, chalk-like line tracks the orange star’s light during a transit, showing a dip in the middle. Text along the line reads “Transits dim the star a little bit once each orbit.” Text along the left axis reads “Starlight,” with “More” above it and “Less” below it. The bottom axis reads “Time” next to an arrow pointing right. Text below the panel reads “But detecting transits in systems with two stars poses a greater challenge.”

2: A larger yellow star appears next to a smaller red star below and to its left. The smaller star is attached to a light blue oval, and an arrow indicates orbital motion in the counterclockwise direction. Text above the stars reads “Binary system. Two stars orbit each other.” The larger star is labeled “Primary (brightest) star,” while the smaller one is labeled “Secondary (companion) star.” At right is another brightness graph, showing a chalky yellow curve with a deep V-shaped notch on the left and a smaller dip on the right. Above the graph are two illustrations of the binary system at left seen from more oblique angles, such that the small star passes in front of (left) and behind (right) the larger star. The left drawing is labeled “Primary eclipse” and an arrow from it points to the deep notch in the graph. The one on the right is labeled “Secondary eclipse,” with an arrow pointing to the small notch in the graph. Above eclipse illustrations, text reads “Viewed from Earth, some binary stars mutually eclipse.” Below the graph, text reads “These larger light variations make it harder to find the tiny dips of transiting planets. Out of hundreds of discoveries, TESS has found only two transiting worlds in binary systems!”

3: In the third panel, a label reads “Orbits aren’t fixed in place. They can slowly rotate, or precess.” The same overhead view of the binary system from the previous panel is shown. The orbital track is now accompanied by two darker copies rotated at slightly different angles. Three magenta lines, one brighter than the others, span the orbit and crosses through the primary star. Two short, thick magenta arrows indicate counterclockwise motion of the lines. A magenta label reads “Line of apsides” and a caption below reads “This line links the companion’s closest and farthest distances (apsides) from the primary star. It precesses with the orbit.” At right is another brightness graph, similar to the one in the previous panel. It has three sets of progressively darker chalky yellow lines, suggesting changes in the eclipse positions over time. The deeper primary eclipses are arriving earlier, while the secondary eclipses are coming later. Text at the top of the graph reads “The slow orbital changes gradually alter when eclipses occur.” Below the graph lie illustrations of three multihued planets, the one on the left resembling a terrestrial world and the others resembling cloudy planets with thick atmospheres. Text below the graph reads “One way orbits precess is from the gravitational effects of additional bodies in the system, like planets!”

4: In the final panel, at left is a cartoon symbolizing many TESS observations of an eclipsing binary system. Text reads “Thousands of TESS brightness measurements have let astronomers find potential planets in eclipsing binaries. These are planet candidates that TESS could not otherwise detect.” The middle image is a larger drawing of TESS, angled so that it appears to be viewing the binary system shown in the previous panel. On the right are light blue outlines of jigsaw puzzle pieces, with six connected at left and two unconnected at right. The final text reads “When confirmed by observations from other facilities, these worlds will help astronomers build a more complete picture of planet formation in our galaxy.”