Teen astronomer finds a planet with two suns
PHOENIX, Ariz. — Sometimes science fiction becomes science fact. For instance: In the Star Wars saga, Luke Skywalker grew up on a world that circled two suns. Now, a teen in New York City has discovered just such a world orbiting a pair of stars far, far away.
Brian Wu, 17, presented his findings here this week at the Intel International Science and Engineering Fair. ISEF was created by Society for Science & the Public in 1950. Its 2019 event, sponsored by Intel, brought together more than 1,800 finalists from 80 countries. (The Society also publishes Science News for Students.)
Storytellers have long imagined worlds that might orbit distant stars, or exoplanets. A little more than 30 years ago, astronomers finally discovered one. Since then, they’ve turned up thousands more. These distant worlds come in many different sizes and some are nothing like any of the planets in our solar system. Now, an 11th-grade student at Horace Mann School in New York City adds a double handful of new objects to the growing tally.
Brian sorted through data collected between 2008 and 2012 by a ground-based telescope in New Mexico. This instrument looked at stars repeatedly during that time. Typically, the telescope returned to view each star once every two weeks or so. And each time, it took a detailed photo of the star in visible light. Embedded in the light spectra coming from the star are loads of dark features called absorption lines, Brian explains. Those narrow, dark lines are created when certain wavelengths of light from the star get absorbed by materials that lie between that star and Earth. Using those lines, scientists can identify what substances had absorbed the starlight. That’s because they know exactly where those lines should show up.
But sometimes those lines don’t appear exactly where they should, Brian says. Instead, they appear shifted. A shifting toward the red end of the spectrum, where the wavelengths are longer, means the star is moving away from Earth. When the star is moving toward Earth, those dark lines will be shifted toward the blue (shorter wavelength) end of the spectrum.
The more the lines have been shifted, the faster the star is moving relative to our planet. This motion-induced shifting of wavelengths is called the Doppler effect. It affects all wavelengths, including sound and microwaves. (This effect is also the foundation for Doppler radar, which shows the movement of wind-driven rain inside clouds.)
By monitoring how the lines in a star’s spectrum have shifted over time, Brian was able to tell if a star was wobbling. If the star wobbled back and forth in a regular fashion — say once every 37 days, for example — that would point to the likely presence of a massive planet or other large body orbiting the star. (The tug of its gravity would induce that wobble.)
In his analysis, Brian focused on the 1,100 or so yellow stars in the photographic survey. Such stars are most similar to our sun. Among these distant stars, Brian found that nine were likely being orbited by giant planets less than 15 times the mass of Jupiter. Another star in the survey is likely circled by something called a brown dwarf. Such a body is typically between 15 and 75 times the mass of Jupiter — too small to become a star. Two of the stars were actually part of a two-star, or binary, system. Those pairs are so far from Earth but so close to each other that they appear to be a single star. Yet the regular changes in their spectra reveal that they’re a wobbling pair.
The most impressive of Brian’s new finds is a circumbinary (Ser-kum-BY-nair-ee) planet. That’s a term for a planet that orbits two stars — just like Tatooine, Luke Skywalker’s home world in Star Wars. Brian’s discovery emerged when he saw the small wobbles caused by the planet on top of the larger wobbles caused by the stars orbiting each other. Brian’s circumbinary planet is the first ever found using Doppler shifting, the teen notes. The other 23 that have been found were discovered by occultations. That’s when a planet passes in front of its parent star, causing a small eclipse — with a brief drop in light reaching Earth-based telescopes.
The circumbinary planet that Brian discovered lies between 400 and 500 light-years from Earth. It orbits its parent stars at a distance of about 90 million miles, his data suggest. It would circle them once every 315 days or so.
From the size of the wobbles of its parent stars, this newfound exoplanet is probably about 2.8 times as massive as Jupiter. That, in turn, likely means the planet is uninhabitable, he notes. But like the large planets in our solar system, the distant super-Jupiter probably has moons, Brian says. And since the planet orbits its parent stars at a distance where water might be liquid year round, those moons might be hospitable for life as we know it.
And that’s science fact, not science fiction.
absorption lines These are typically dark lines that can show up in a continuous spectrum of electromagnetic radiation (light). They mark where some frequencies of light from the source have been absorbed. They develop when some material (such as interstellar gas, dust clouds or some outer part of a star’s atmosphere) lies between the light source and the observer.
astronomy The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.
binary Something having two integral parts.
brown dwarf A would-be star that never became massive enough to sustain nuclear fusion and burn brightly.
circumbinary (in astronomy) An adjective that describes a planet that orbits two stars.
Doppler effect A perceived change in the frequency of some waves (sound, microwaves or light, for instance) when the distance between the source and the receiver is increasing or decreasing. It’s best known as the explanation for why a police siren sounds differently when the vehicle is racing toward you versus when it is moving quickly away from you.
eclipse This occurs when two celestial bodies line up in space so that one totally or partially obscures the other.
engineering The field of research that uses math and science to solve practical problems.
exoplanet Short for extrasolar planet, it’s a planet that orbits a star outside our solar system.
gravity The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
induce To produce or cause something to happen. In physics, electromagnetic induction is the production of electricity with varying magnetic fields.
Jupiter (in astronomy) The solar system’s largest planet, it has the shortest day length (10 hours). A gas giant, its low density indicates that this planet is composed of light elements, such as hydrogen and helium. This planet also releases more heat than it receives from the sun as gravity compresses its mass (and slowly shrinks the planet).
light-year The distance light travels in one year, about 9.48 trillion kilometers (almost 6 trillion miles). To get some idea of this length, imagine a rope long enough to wrap around the Earth. It would be a little over 40,000 kilometers (24,900 miles) long. Lay it out straight. Now lay another 236 million more that are the same length, end-to-end, right after the first. The total distance they now span would equal one light-year.
mass A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.
microwaves An electromagnetic wave with a wavelength shorter than that of normal radio waves but longer than those of infrared radiation (heat) and of visible light.
moon The natural satellite of any planet.
occultation A celestial eclipse-like event in which an object that appears large from Earth, such as the moon, obscures a smaller-seeming object, such as a distant star.
orbit The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.
planet A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood.
radar A system for calculating the position, distance or other important characteristic of a distant object. It works by sending out periodic radio waves that bounce off of the object and then measuring how long it takes that bounced signal to return. Radar can detect moving objects, like airplanes. It also can be used to map the shape of land — even land covered by ice.
science fiction A field of literary or filmed stories that take place against a backdrop of fantasy, usually based on speculations about how science and engineering will direct developments in the distant future. The plots in many of these stories focus on space travel, exaggerated changes attributed to evolution or life in (or on) alien worlds.
solar system The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.
spectrum (plural: spectra) A range of related things that appear in some order. (in light and energy) The range of electromagnetic radiation types; they span from gamma rays to X rays, ultraviolet light, visible light, infrared energy, microwaves and radio waves.
star The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
sun The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.
survey To view, examine, measure or evaluate something, often land or broad aspects of a landscape.
telescope Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.
wavelength The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.