Is there life on Europa, Jupiter's icy moon?
How to help as an amateur to answer this question.
Europa is, along with Io, Ganymede and Callisto, one of Jupiter's four largest satellites, known as Galileans. NASA plans to launch the CLIPPER probe in October 2024 to reach Europa in April 2030 and study it from very low altitude (25 km above the surface).
This and other missions to Jupiter's moons would not be possible without a thorough knowledge of their orbits. Let's see how it is possible to achieve, by observing something called the "mutual phenomena", high accuracy in the position of Galilean satellites.
When one Galilean satellite projects its shadow onto another or when, from the perspective of the Earth, one satellite passes in front of another, a "mutual phenomenon" is taking place. The first case mentioned is an eclipse and the second an occultation. For this to occur, either the Sun or the Earth has to pass through the common plane of the orbits of Jupiter's satellites, which happens every 6 years or so. The last time was in 2021 and the next time will be in 2026.
Actually, the mutual phenomena (called PHEMU) are photometric events. They involve obtaining a light curve that represents the time evolution of the light we receive during an eclipse or an occultation between two of the satellites. These measurements must be made with a very precise time base and from the obtained light curve experts are able to calculate astrometric data with accuracies of the order of 45km.
It is marvellous how a light curve (photometry) makes it possible to deduce the position of satellites (astrometry) with precision, which has important consequences for the knowledge of satellite orbits and is key to the success of space missions such as that of the CLIPPER probe.
With this ambitious and interesting objective, the AAM (Agrupación Astronómica de Madrid) formed a working group many months before the mutual phenomena of 2021, to prepare these observations and to be able to report the light curves to the researchers.
The result of so much effort and dedication has been the obtaining by 7 observers of the AAM, including myself, of a very significant part of the total number of observations, about 25% of all the observations made worldwide.
Below, I show some of the light curves I obtained (the solid line represents the expected evolution and the dots the measurements obtained).
These data are captured with an SC 8" and an ASI1600mm camera, as well as a time base from a GPS-based Stratum 1 Local Server (https://www.observatorio-majadahonda.com/time-server).
In addition to all that we have enjoyed and learned during the 2021 PHEMU campaign, the AAM observers have the satisfaction of being part of the scientific paper that compiles the results of the campaign, which I include below.