Free Astronomy Magazine September-October 2022

30 SEPTEMBER-OCTOBER 2022 ASTRO PUBLISHING uring its temperature from Earth is no easy task. “This type of study is only possible with sensitive infrared images from large tel- escopes like the VLT that can observe Nep- tune clearly, and these have only been avail- able for the past 20 years or so,” says co- author Leigh Fletcher, a professor at the Uni- versity of Leicester. Around one third of all the images taken came from the VLT Im- ager and Spectrome- ter for mid-InfraRed (VISIR) instrument on ESO’s VLT in Chile’s Atacama Desert. Be- cause of the tele- scope’s mirror size and altitude, it has a very high resolution and data quality, of- fering the clearest images of Nep- tune. The team also used data from NASA’s Spitzer Space Telescope and images taken with the Gemini T he image of the planet Neptune on the left was obtained during the testing of the Narrow- Field adaptive optics mode of the MUSE instrument on ESO’s Very Large Telescope. The image on the right is a comparable image from the NASA/ESA Hubble Space Telescope. Note that the two images were not taken at the same time so do not show identical surface [ESO/P. Weilbacher (AIP)/NASA, ESA, and M.H. Wong and J. Tollefson (UC Berkeley)] T he evolution of thermal images taken from Neptune using the VLT’s VISIR instrument. The images, taken between 2006 and 2021, show Neptune grad- ually cooling down, before a dramatic heating of its south pole in the last few years. [ESO/M. Roman] South telescope in Chile, as well as with the Subaru Telescope, the Keck Telescope, and the Gemini North telescope, all in Hawai’i. Because Neptune’s temperature vari- ations were so unexpected, the as- tronomers do not know yet what could have caused them. They could be due to changes in Neptune’s stratospheric chemistry, or random weather patterns, or even the solar cycle. More observations will be needed over the coming years to ex- plore the reasons for these fluctua- tions. Future ground-based tele- scopes like ESO’s Extremely Large Telescope (ELT) could observe tem- perature changes like these in greater detail, while the NASA/ ESA/CSA James Webb Space Tele- scope will provide unprecedented new maps of the chemistry and temperature in Neptune’s atmos- phere. “I think Neptune is itself very in- triguing to many of us because we still know so little about it,” says Roman. “This all points towards a more complicated picture of Nep- tune’s atmosphere and how it changes with time.” !