WHAT’S IN THE ATMOSPHERE OF WASP-39 B?
EVEN AS PLANETARY SCIENTISTS work to reveal our solar system’s many tantalizing secrets, the over 5,000 known exoplanets in our galaxy remain a mystery. While we typically know their orbits and often their sizes and masses, most other information lies beyond the reach of Earth-based telescopes and even Hubble. But JWST has already started to change the status quo.
How important are exoplanets to JWST scientists? They allocated nearly one-quarter of observing time during Cycle 1 to the study of these worlds and the materials that form them.
Although not designed to discover exoplanets, JWST has confirmed one around the star LHS 475, a red dwarf located 41 light-years from Earth in the constellation Octans. NASA’s Transiting Exoplanet Survey Satellite (TESS) hinted that this star might harbor a planet, but it took the new space telescope to confirm the minuscule dip in brightness caused by the planet crossing in front of, or transiting, the star’s disk. The planet appears to be rocky, with a diameter just 1 percent smaller than Earth, though the resemblance to our home world stops there. It orbits its sun in only two days and boasts a temperature a few hundred degrees warmer than Earth.
However, JWST’s real strength comes from its ability to analyze the atmospheres of exoplanets. To accomplish this, the telescope must observe transits with its powerful spectrographs. As a planet passes between Earth and its host star, its atmosphere filters out some wavelengths of the starlight. Because every atom and molecule has a distinct spectral fingerprint, this allows astronomers to study the chemical makeup of these worlds.
Most of the molecules that interest exoplanet researchers lie in the infrared part of the spectrum. While Hubble could tease scientists with its observations, JWST will satisfy their appetites.
The observatory’s first exoplanet target was WASP-39 b, a hot gas giant planet orbiting a Sun-like star 700 lightyears away in the constellation Virgo. JWST’s superb resolution revealed water, sulfur dioxide, carbon monoxide, sodium, potassium, and — for the first time ever in any exoplanet — carbon dioxide. The planet glows at a temperature of 1,650 degrees Fahrenheit (900 degrees Celsius) not because of a runaway greenhouse effect, but because it orbits just 4.52 million miles (7.27 million km) from its star. (In comparison, Mercury orbits nearly 36 million miles [57.9 million km] from the Sun.)