Flared! How a planetary ‘neighbor’ may have been fried | Science News for Students

Flared! How a planetary ‘neighbor’ may have been fried

Likely repeated radiation, spewed by its home star, scorches most hope that Proxima b can host life
Mar 28, 2018 — 6:45 am EST
Proxima Centauri flare
An artist’s view of a gigantic flare leaving Proxima Centauri in March 2017. This massive release of energy appears to fizzle hopes that its nearby Earth-mass planet can host life.
ROBERTO MOLAR CANDANOSA/CARNEGIE INSTITUTION FOR SCIENCE, SDO/NASA, JPL/NASA

The sun’s nearest planet-hosting neighbor has a temper. A new analysis shows this star — Proxima Centauri — released a gigantic flare in March 2017. And that’s bad news in terms of hopes for finding life on its planet, Proxima b.

Observations show that over one 10-second period, the star got 1,000 times brighter. Then it dimmed again. This event can best be explained by an enormous stellar flare, explains a team of scientists in the February 26 Astrophysical Journal Letters. A flare is an intense — indeed, explosive — burst of energy by a star.

Because Proxima b is so much closer to its star than Earth is to our sun, the flare would have blasted that exoplanet with 4,000 times more radiation than Earth typically gets from our sun’s flares.

Meredith MacGregor is an astronomer with the Carnegie Institution for Science in Washington, D.C. She also co-authored the new paper. “If there are flares like this at all frequently, then [Proxima b] is likely not in the best shape,” she says.

Just four light-years away, Proxima b has a mass about the same as Earth’s. It likely also has temperatures suitable for liquid water. And that’s why Proxima b was quickly identified as one of the most interesting candidates for hosting life outside our solar system. But its star is what’s known as an M dwarf. Such small dim stars are well known to be prone to flares that could rip away a planet’s atmosphere.

MacGregor was part of a team that reanalyzed data from a recent study. That research had been led by astronomer Guillem Anglada. He works in Spain at the Institute of Astrophysics of Andalusia in Granada. Anglada’s group used the Atacama Large Millimeter Array telescopes in Chile to observe Proxima Centauri. That team saw extra light being scattering in all directions. The group interpreted it as coming from a glittering dust ring. Anglada's team reported this November 15 in Astrophysical Journal Letters.

But those researchers had averaged the light output over 10 hours of viewing. This would smear out any short-term explosive change in the star’s brightness — such as a bright flare.

MacGregor’s team took a second look at these data. And it found that all the excess light came from a two-minute period on March 24. A massive flare explains all the extra light, MacGregor now says.

Anglada says he and his colleagues are aware of the March 24 flare. As a result, they currently are revising their original claim. But, that astronomer argues, the flare can’t account for all the extra light. So he still thinks the dust-ring theory might hold up.

Power Words

(for more about Power Words, click here)

array     A broad and organized group of objects. Sometimes they are instruments placed in a systematic fashion to collect information in a coordinated way.

astronomy     The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.

astrophysics     An area of astronomy that deals with understanding the physical nature of stars and other objects in space. People who work in this field are known as astrophysicists.

atmosphere     The envelope of gases surrounding Earth or another planet.

colleague     Someone who works with another; a co-worker or team member.

data     Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning.

exoplanet     Short for extrasolar planet, it’s a planet that orbits a star outside our solar system.

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.

M dwarf     The most common type of star in the Milky Way. M dwarfs are smaller, cooler and fainter than yellow dwarfs, of which our sun is an example.

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.

radiation     (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.

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.

stellar flare     An intense burst of energy by a star. When it happens to our sun, it's known as a solar flare.

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.

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.

theory     (in science) A description of some aspect of the natural world based on extensive observations, tests and reason. A theory can also be a way of organizing a broad body of knowledge that applies in a broad range of circumstances to explain what will happen. Unlike the common definition of theory, a theory in science is not just a hunch. Ideas or conclusions that are based on a theory — and not yet on firm data or observations — are referred to as theoretical. Scientists who use mathematics and/or existing data to project what might happen in new situations are known as theorists.

Citation

Journal:​ M. MacGregor et al. Detection of a millimeter flare from Proxima CentauriAstrophysical Journal Letters. Published February 26, 2018.

Journal:​ G. Anglada et al. ALMA discovery of dust belts around Proxima CentauriAstrophysical Journal Letters. Published November 15, 2017.