The field of astronomy is about to be revolutionized, thanks to the introduction of Extremely Large Telescopes that rely on primary mirrors measuring 30 meters (or more) in diameter, adaptive optics (AO), coronographs, and advanced spectrometers. This will include the eponymously-named Extremely Large Telescope (ELT), the Giant Magellan Telescope (GMT), and the Thirty Meter Telescope (TMT). These telescopes will enable astronomers to study exoplanets using the Direct Imaging (DI) method, which will yield valuable data on the composition of their atmospheres.
According to a new study by a team of researchers from Ohio State University (OSU), these telescopes will also allow astronomers to study “ultracool objects,” like very low-mass stars (VLMs), brown dwarfs, and exoplanets. In addition to being able to visualize magnetic starspots and determine the chemical compositions of these objects, ELTs will be able to reveal details about atmospheric dynamics and cloud systems. These types of studies could reveal a wealth of information about some of the least-studied objects in our Universe and significantly aid in the search for life beyond our Solar System.
The study was performed by Michael K. Plummer and Ji Wang, a Ph.D. student and professor of astronomy at OSU (respectively), as part of Plummer’s doctoral thesis. Plummer is also an officer and pilot who previously studied at the United States Air Force Academy, while Wang specializes in the creation of sensitive instruments that allow for more-detailed exoplanet studies. The paper that describes their findings, titled “Mapping the Skies of Ultracool Worlds: Detecting Storms and Spots with Extremely Large Telescopes,” was recently accepted for publication in The Astrophysics Journal.
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The study of ultracool objects is a burgeoning field in astronomy, something that has been very difficult using optical telescopes. Thanks to advances in infrared and radio astronomy, astronomers have learned much about these objects in recent years, allowing them to better understand the range and nature of objects in our Universe. As Plummer told Universe Today via email:
“Ultracool dwarfs, including the lowest-mass stars and brown dwarfs, have effective temperatures that allow condensates to form in their atmospheres. These condensates can include metal and silicate clouds. It is thought that at the spectral L/T transition around 1300 K, the clouds begin to rain out, creating patchy atmospheric features. For rapid rotators, this may lead to high variability in the spectral and photometric signals we observe for these objects.”
Looking at the capabilities of next-generation telescopes, Plummer and Wang considered how their highly-sensitive spectrometers, infrared imaging capabilities, and improved signal-to-noise ratio would allow for more detailed studies of VLMs, brown dwarfs, and exoplanets. These include Transit Spectroscopy (a variation on Transit Photometry), where planets periodically transit in front of their stars (relative to the observer), causing light to pass through their atmosphere. There’s also Direct Spectroscopy, a variation on the Direct Imaging method.
In this case, astronomers rely on coronagraphs to block out the light of a star, making light reflected by exoplanet atmospheres and surfaces visible to their instruments. In both cases, Plummer and his colleagues considered what types of atmospheric features these observatories and their advanced instruments would be able to visualize. As Plummer added:
“It has also been proposed that banded features (like we see on Jupiter) may be responsible for the observed variability. Doppler imaging can map large scale weather features on these ultracool targets, shedding light on the thermal, chemical, and dynamical structure of substellar objects. This can help us to understand if these objects’ atmospheres are predominantly banded, patchy, or a combination of both regimes.”
For their study, Plummer and Wang addressed the spectrographs 30-meter-class telescopes will use to conduct stellar and exoplanet studies. This includes the GMT’s Consortium Large Earth Finder (G-CLEF), a visible light echelle spectrograph with adaptive optics that will conduct Radial Velocity (RV) measurements that are accurate to at least 50 cm/s. These capabilities will allow astronomers with the GMT to characterize the most metal-poor stars, measure the masses of exoplanets (as small as Mars-sized) around M-type (red dwarf) stars, and detect oxygen gas in exoplanet atmosphere’s using transmission spectra.
Second, there’s the TMT’s Multi-Objective Diffraction-limited High-Resolution Infrared Spectrograph (MODHIS), a diffraction-limited high-resolution infrared facility. As part of the Narrow Field Infrared Adaptive Optics System (NFIRAOS), MODHIS will conduct precision RV measurements (30 cm/s or more) and obtain spectra from exoplanet atmospheres using the Tranist Method and Direct Imaging (thanks to the TMT’s coronagraph instrument). It will further measure exoplanet rotations, radial velocities, cloud dynamics, and weather.
Third, there’s the ELT’s Mid-Infrared ELT Imager and Spectrograph (METIS), which covers the entire infrared wavelength range and will be used to study everything from Solar System bodies to stars, protoplanetary disks, exoplanets, and distant galaxies. Based on their assessment of these instruments and their capabilities, Plummer and Wang illustrated the kind of research they would enable (and its immense implications). As Plummer explained:
“Upcoming ELTs and their planned spectroscopic instruments will provide the requisite signal-to-noise ratio and spectral resolution to create Doppler imaging maps for faint brown dwarfs and, likely, the brightest exoplanets, which also are at large orbital distances from their host stars. Doppler imaging extrasolar giant planets will help us to understand how gas giant atmospheres differ from those observed within our own solar system.
“Brown dwarfs also serve as excellent analogs for extrasolar gas giant planets due to their similar temperature, size, and spectral classes. Young, low surface gravity brown dwarfs are particularly interesting in this regard as they appear to have similarly red spectra (likely from optically thick clouds) as many of the gas giants we have directly imaged (e.g. the HR 8799 planets).”
Some incredible breakthroughs are expected in the coming years, thanks to next-generation telescopes and instruments revealing more and more about the Universe. Astronomers today also benefit from increased participation from the general public and collaboration between observatories and citizen scientists – who help sort through the heaps of scientific data. Machine learning and more advanced algorithms are also being used more frequently, greatly increasing the rate at which new objects and exoplanets are discovered.
In addition to the volumes of information this will provide, there is also the way that more sophisticated tools and methods are causing the transition from discovery to characterization. Not only is there likely to be an exponential increase in the number of confirmed exoplanets and other bodies, but there’s also the fact that scientists will be able to get a much closer look at them. With the ability to determine chemical compositions and even see weather patterns, scientists can determine if distant exoplanets are “habitable.”
Who knows? With any luck, the data could reveal the first evidence of life beyond Earth and maybe even an advanced civilization or two!
Further Reading: arXiv