Mercury is one of those planets of our solar system we don’t talk about much. Nothing like Venus being often visible with naked-eye as the first “star” of the night. Nothing like Mars who concentrate many interesting space missions and probes, or the giants Jupiter and the magnificent Saturn. Even Pluto (not a planet anymore, but a so-called dwarf planet) recently made big headlines with the stunning new images obtained by the New Horizons mission. Remain Neptune, Uranus and… Mercury, the closest planet to our Sun.
I mean, really close. And it matters, for our story.
Just a side note: the proximity of Mercury with our Sun is also the cause of an interesting phenomenon, explained only since Einstein’s General Relativity.
Back to our story. Say you are participating to a new mission of the European Space Agency to launch a probe on Mercury-the-not-so-well-known. Say you need to prepare this mission with ground observations, in order to better understand the planet when designing and calibrating the instruments and the measurement devices that will fly with the probe. What do you do? Like every professional astronomer, you write a telescope-time proposal.
The whole process of obtaining observing time on large telescopes will require its own blog post. Let’s jump into to what happens in the last phase of the process… since I was an actor of it, in 2005.
(Note, today, the mission Beppi-Colombo has been launched, and is “en route” for Mercury!)
Let’s say you are a young astronomer, with a Ph.D. in astrophysics, who work as “support astronomer” in a great observatory in La Silla, in Chile. At that time, every support astronomer was attached to a given instrument. Mine was called EMMI, for ESO Multi-Mode Instrument, a versatile, multi-filter, multi-wavelength, multi-spectroscopic & imaging modes instrument (picture below).
Part of your job is to evaluate telescope-time proposals that have been selected by the scientific committee. At the very large majority of the time, these selected proposals are the excellent ones among the mostly excellent and large pile of proposals, and the scientific committee decided to give them the telescope time they requested. Only the “technical feasibility” remains to be checked, by people like myself at that time, to ensure that the selected instrument is actually capable of executing the observations.
So picture this. You’re in the large control room in La Silla, confortably seated at the large table, with all these proposals printed in front of you. To evaluate the technical feasibility, you need to read the whole proposal, including the science justification, in order to understand what the requesters want to achieve. It’s a fairly long process, and requires a good amount of mental energy.
And I remember that one. About Mercury. That was clearly a technically-messy description of what the instrument was supposed to do. My impression was that these people didn’t really read the EMMI documentation, nor they cared about. Clearly, I couldn’t really figured out what they wanted to do, technically speaking. So exceptionally, I rejected the proposal, with a written justification explaining how the requested observations couldn’t be made.
Well… I was playing the gatekeeper, with my little power. How funny it is to understand today the lack of maturity I had. But life gave me a lesson.
A few weeks later, I was back to La Silla for a given “turno” of about 10 days. And I was designated “Shift Leader” for a few days. This was not the first time, and the role was switching between astronomers. Not much to actually lead, given the high level of professionalism of all the people up there, but one additional responsability: read the emails of the observatory mailing address.
And suddenly, ping! Email from the Principal Investigator (PI) of the Mercury proposal, complaining that his proposal had been rejected by the observatory. I kept my mouth shut (it was not my role to answer, the observatory was simply in CC, and nobody outside knew it was me reading…). Interestingly, some of the science leadership people at ESO accepted the complain of the PI, and turned the request back to La Silla, asking not to judge a poor technical feasbility but rather… help them define the right one!
And guess who was in charge of helping them? One of the EMMI specialists of course. And it fell upon… me! (We were only a handful of EMMI “specialists”).
After an exchange of a few emails, we finalised an operational setup, and we were ready to observe. The tricky thing was to observe … Mercury, you remember? Mercury which is always close to our Sun. I mean, it is also very true visually speaking, obviously. That is, we cannot observe Mercury in the middle of night when it is high in the sky, as we do with normal targets, because… it never happens! We can observe Mercury only right after sunset, or very shortly before sunrise. And not for a long time, because it goes quickly below the horizon in the evening, or because the sky is becoming too bright, in the morning!
And of course, you need to turn your telescope to it, hence it will be pointing at a very low altitude. When you have a 4-meter class telescope like the NTT, and a 2-tons mirror, it is not something you take lightly!
But why on Earth would you take a 4-meter class telescope to observe Mercury?!
Because the goal was to find estimations of the amout of some metallic atoms in Mercury’s atmosphere, through the width of spectral lines. And spectroscopically, these can be seen in the very blue part of the spectrum, close to ultra-violet (around 3200 Angstroem – yes, I will also do a post on crazy units astronomers use). And these spectral lines are very narrow. Hence, you need very high spectral resolution to distinguish them, and thus as much light as you can, because it will be highly spread out over the detector. Moreover, detectors aren’t efficient in the blue (it’s related to the poor silicium capability of absorbing blue photons). But you don’t have much time for observing!!! Just a few minutes at dawn, and likewise at sunrise.
Hence, you need a very large collector! For instance, a 4-meter class telescope, like the New Technology Telescope (NTT), in La Silla.
All in all, we managed to do it. It was quite exceptional, and today I am very proud to put this in my hunting table.
Guess what is the best conclusion? Once the people of the proposal received the raw data obtained at the observatory, they needed to “reduce” it (it means processing the raw data to extract the scientific one). Who’s best to do that? A specialist of the instrument! These people contacted me, and I reduced the data for them, with their help. And as a participant of that observing campaign, they included me in the final publication:
What a happy ending!
P.S. This post is obviously dedicated to my former colleagues A. Doressoundiram, F. Leblanc and S. Erard.
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