now that has begun science operations, some of the main targets of the James Webb Space Telescope will be exoplanets. The telescope can identify and examine planets outside our solar system, and can even look at their atmospheres to see what they are made of. That will give us more information than ever about the diversity of types of planets that exist.
If you look at the data on exoplanets that have been studied in the past and will be studied in the future, you will notice that many of them are of the type called hot Jupiter. Unlike rocky planets like Earth, Mars, or Venus, hot Jupiters are gas giants that orbit very close to their host stars. With a year on a hot Jupiter lasting only a few days or even a few hours, they are close enough to their stars to experience very high temperatures of thousands of degrees Celsius. And they range in mass from slightly lighter than Jupiter to more than ten times its mass.
As strange as these planets sound, and as different as they are from anything in our solar system, studying them could be crucial to learning how planetary systems form. Scientists aren’t yet sure how hot Jupiters get, as they seem to orbit too close to their stars to have formed there. Perhaps they formed farther out and were then pulled into a closer orbit, or perhaps tidal forces affected their orbits. We don’t know for sure.
Another reason to study these planets is that they tend to be puffy, as they have the mass of a planet but can be the size of a star. If a planet has a puffy atmosphere, it’s easier to get data about that atmosphere using spectroscopy, in which light from the star passes through the atmosphere and is analyzed to see what that atmosphere is made of.
One such hot Jupiter with a puffy atmosphere is WASP-121b, a monstrous planet with a temperature of over 2,000 degrees Celsius. “It has a very bloated, bloated atmosphere. And it also has a very clear atmosphere because it’s too hot for clouds and haze to form, which makes it a very tempting target for transmission spectroscopy because there’s plenty of atmosphere for the parent star’s light to shine through. ”, explained Steph Merritt of Queen’s. University of Belfast, which studied the planet using a method called Doppler spectroscopy, in a talk at the 2022 National Astronomy Meeting.
However, it is not easy to study the atmosphere of a planet millions of kilometers away. Both ground-based telescopes and Hubble have done previous work on exoplanet atmospheres, but there are limits to what these tools can tell us. Hubble has been used to study the atmosphere of hot Jupiter WASP-17b, for example, but the observations only captured part of the transit (the period when the planets pass in front of the star, making spectroscopy possible).
This makes data analysis difficult, as there is a lot of uncertainty about what specific elements make up WASP-17b’s atmosphere. “All we can say for sure about WASP-17b is that the current data shows a safe direction of H2O and a tentative hint of CO2,” said Lili Alderson of the University of Bristol, who worked on a new analysis of the data. of the planet. , in the same meeting.
WASP-17b will be one of the first targets James Webb studies in his first year, helping to reveal more about its atmosphere by collecting more data in the infrared range, in addition to the optical data collected by Hubble. “We need the combination of high-quality optical and infrared data to properly understand the atmospheres of these planets,” Alderson said.
An example of the rarity of hot Jupiters is that many of them show a phenomenon called inverted atmospheres, in which temperatures in the upper atmosphere increase with altitude. You’d expect atmospheres to get cooler as you go higher, unless you have a special situation like Earth’s ozone layer. The current theory is that metallic elements found in Jupiter’s hot atmospheres, such as titanium oxide, vanadium oxide, and iron hydride, which absorb starlight and heat the atmosphere, are similar to our own. ozone layer.
As much as astronomers have learned so far about hot Jupiters, there is still much more to learn from James Webb. If we can figure out how these strange planets formed, we’ll learn more about the formation of other systems, including our own solar system. However, even with this additional data, it may not be enough to fully understand this strange and alien world.
“Planets are really complicated!” Alderson said. “We can’t always come to bold and exciting conclusions with a simple set of data.”