Researchers use exoplanet hunter VLT to study Jupiter’s winds

For the first time, an instrument capable of finding planets light years away has been used on an object in the solar system, as part of a study of Jupiter’s winds.

We find ourselves in an era where it has become almost commonplace to discover planets orbiting another star, with more than 5,000 already recorded. The first distant worlds to join this list were mainly giant planets, similar but also very different in many respects from Jupiter and Saturn.

Astrophysicists have already begun to obtain data on the atmospheres of exoplanets, but fundamental questions about the atmosphere of the solar system’s largest planet still remain unanswered. To understand what is happening in Jupiter’s clouds and air layers, it is necessary to study it over time through continuous observations.

For the first time, an instrument developed to find and analyze worlds light years away, exoplanets, has been pointed at a target in the solar system, 43 light minutes from Earth: the planet Jupiter.

Researchers from the Institute of Astrophysics and Space Sciences (IA) of the Faculty of Sciences of the University of Lisbon (Portugal) (Ciências ULisboa) used the ESPRESSO spectrograph installed on the VLT telescope of the European Southern Observatory (ESO) to measure wind speed. on Jupiter. The results are now published in the journal Universe.

The method developed by the team is called Doppler velocimetry and is based on the reflection of visible sunlight from clouds in the atmosphere of the target planet. This reflected light is bent in wavelength proportional to the speed at which the clouds are moving relative to the telescope on Earth. This gives the instantaneous wind speed at the observed point.

The method now used with ESPRESSO was developed by the AI ​​Planetary Systems Research Group, along with other spectrographs, to study the atmosphere of Venus. Researchers have been measuring the winds of this neighboring planet and have been contributing for several years to the modeling of its general atmosphere.

The exploratory application of this method with a “high-end” instrument such as ESPRESSO has resulted in a success that opens new horizons to the knowledge of our cosmic neighborhood. This work affirms the feasibility of systematically monitoring the most distant atmospheres of gaseous planets.

For five hours in July 2019, the team pointed the VLT telescope at Jupiter’s equatorial zone, where light clouds are found at a higher altitude, and at that planet’s northern and southern equatorial belts, which correspond to descending air and forms bands of dark, warmer clouds in a deeper layer of the atmosphere.

“Jupiter’s atmosphere, at the cloud level visible from Earth, contains ammonia, ammonium hydrosulfide and water, which form distinct red and white bands,” explains Pedro Machado , of AI and Ciências ULisboa. “The upper clouds, located in the pressure zone of 0.6 to 0.9 bar, consist of ammonia ice. Water clouds form the densest, lowest layer, and have the strongest influence on the dynamics of the atmosphere”, adds the researcher.

With ESPRESSO, the team was able to measure winds on Jupiter from 60 to 428 km/h with an uncertainty of less than 36 km/h. These observations, applied with a high-resolution instrument to a gaseous planet, have their challenges: “One of the difficulties centered on “navigation” on the disk of Jupiter, that is to say knowing exactly to which point of the planet’s disk we were pointing, due to the enormous resolution of the VLT telescope”, explains Pedro Machado.

“In the research itself, the difficulty was linked to the fact that we determined the winds with a precision of a few meters per second while the rotation of Jupiter is of the order of ten kilometers per second at equator and, to complicate things because it is a gaseous planet, and not a rigid body, it rotates at different speeds depending on the latitude of the point we observe,” adds the researcher.

To verify the effectiveness of Doppler velocimetry from ground-based telescopes in measuring winds on Jupiter, the team also gathered measurements obtained in the past to compare the results. Most existing data have been collected by space instruments and used a different method, which involves obtaining average wind speed values ​​by tracking cloud patterns in images captured at nearby times.

The consistency between this history and the values ​​measured in the study now published confirms the feasibility of implementing Doppler velocimetry in a program to monitor Jupiter’s winds from Earth.

The monitoring will allow the research team to collect data on how winds change over time and will be essential for developing a reliable model of the overall circulation of Jupiter’s atmosphere.

This computer model should reproduce the differences in winds depending on latitude and Jupiter’s storms to help understand the causes of the atmospheric phenomena we observe on this planet. Conversely, the model will help prepare future observations with information on the pressure and altitude of clouds in the telescope’s sight.

The team intends to extend observations with ESPRESSO to greater coverage of the disk of the planet Jupiter, as well as to temporally collect wind data throughout the planet’s rotation period, i.e. near from 10 a.m. Restricting observations to certain wavelength ranges will also allow winds to be measured at different altitudes, thereby obtaining information about the vertical transport of air layers.

Once the technique is mastered for the solar system’s largest planet, the team hopes to apply it to the atmospheres of other gaseous planets, with Saturn as the next target.

The success of these observations with ESPRESSO is important at a time when its successor, ANDES, is being designed for the future Extremely Large Telescope (ELT), also from ESO and currently under construction in Chile, but also for the future JUICE mission, from the European Space Agency, dedicated to Jupiter and which will provide additional data.