Artist's concept of a hot Jupiter extrasolar world. Credit: NASA, ESA and L. Hustak, STScI
A team of international scientists used the Gemini Observatory telescope in Chile to measure the atmospheric concentration of water and carbon monoxide on a planet located approximately 340 light years away.
The team was led by Assistant Professor Michael Line from Arizona State University's School of Earth and Space Exploration. Recent results were published in Nature.
Exoplanets are a group of thousands of planets that exist outside our solar system. To study how exoplanets formed and their differences from planets in our solar system, scientists use both ground-based and space telescopes.
Line and his team studied planet "WASP77Ab", a type exoplanet known as a hot Jupiter. They are similar to Jupiter in our solar system, but have temperatures higher than 2,000 degrees Fahrenheit.
The team then measured the atmosphere of the planet to determine which elements were present. This was done in comparison with the star it orbits.
Line stated that hot Jupiters, because of their size and temperature, are great laboratories for testing planet-formation theories and measuring atmospheric gases.
Although we can't send spacecraft to other planets in our solar system yet, scientists can observe the light coming from these exoplanets using telescopes. They can use either a telescope in space like the Hubble Space Telescope or a telescope on the ground like the Gemini Observatory telescopes to view this light.
Line and his team were heavily involved in the measurement of the atmospheric compositions exoplanets using Hubble. However, it was difficult to obtain these measurements. There is a lot of competition for telescope time. Hubble's instruments do not measure water, so the team had to collect measurements of carbon monoxide.
Here is where the team reached out to the Gemini South telescope.
Line stated that Line needed to find a different way to answer our questions. "And our analysis on the capabilities of Gemini South showed that we could obtain extremely-precise atmospheric measures."
Gemini South, a telescope measuring 8.1 meters in diameter, is located on Cerro Pachn (a mountain in Chile's Andes), where there is very little cloud cover and dry air. The NOIRLab (National Optical-Infrared Astronomy Research Laboratory) operates it.
Scientists can calculate a planet's orbital velocity by measuring the Doppler shift in the right column. Information about the amount of gases in the atmosphere can be found in the strength of the planet signal, as shown in the middle column. It is based on the expected apparent velocity (navy-dashed curve) of the planet. Credit: P. Smith / M. Line / S. Selkirk / ASU
The team used the Gemini South telescope with an instrument called Immersion GRating INfrared Spectrometer, to observe the exoplanet's thermal glow as it orbited its host star. They were able to gather information about the atmosphere's composition and relative amounts.
Scientists can also use spectrometers or telescopes (such as IGRINS on Gemini South) to measure different gases on other planets.
Line stated that trying to determine the composition of planetary atmospheres with fingerprints is similar to solving a crime using fingerprints. Line said that a smudged fingerprint does not really help to narrow down the problem, but that a clean, neat fingerprint can provide a unique identifier for who committed the crime.
The Hubble Space Telescope gave the team only a few fuzzy fingerprints. IGRINS on Gemini South provided a complete set of fingerprints.
The team then was able to calculate the relative levels of carbon and oxygen in the atmosphere at WASP-77Ab with precise measurements of water and carbon monoxide.
Line stated that the amounts were comparable to the expectations of Line and about the same as the star host's.
It is not only a technical accomplishment to obtain extremely precise gas abundances from exoplanet atmospherics, especially using a ground-based telescope. However, this may help scientists search for life on other worlds.
Line stated that this work is a "pathfinder demonstration" for how biosignature gases such as oxygen and methane can be measured in potentially habitable planets in the near future.
Line and his team plan to continue this analysis on many more planets, and create a "sample of atmospheric measurements" on at least 15 additional planets.
"We now have the ability to obtain similar gas abundance precisions as those planets in our solar system." Line stated that measuring the abundances in carbon and oxygen (and other element) in the atmospheres on a larger number of exoplanets gives us a lot of context to understand the evolution and origins of gas giants such as Jupiter and Saturn.
They are also excited about the future of telescopes.
Line stated, "If we are able to accomplish this with current technology, imagine what we will do with the new telescopes like Giant Magellan Telescope." It is possible that this same method can be used by the end this decade to detect potential signs of life on planets similar to Earth.
More information: Michael R. Line and colleagues, A solar C/O, sub-solar metallity in a hot Jupiter atmospheric, Nature (2021). Information from Nature Michael R. Line and colleagues, A solar C/O, sub-solar metallity in a hot Jupiter atmospheric, (2021). DOI: 10.1038/s41586-021-03912-6
