Thursday, 7 July 2011

Pluto and Charon

I'm currently taking a 24-hr break from the summit of Mauna Kea. It's ironic because for the last few months since UKIRT switched to remote operations I've really missed being on the mountain, but in a fit of telescope and instrument commissioning I've been up there for the last week and needed a short break at sea level before heading back up there again for the majority of the next 10 days. Anyway, the cats missed me...

We're hoping to do a little planetary science over the next week or so using an instrument designed and built by NASA scientists called Celeste. It's a mid-infrared high-resolution spectrograph designed to identify molecules in planetary atmospheres. I'm no planet expert but do have a background in spectroscopy and mid-infrared astronomy so am eager to help make this little venture work before we go back to surveying the infrared universe for UKIDSS with WFCAM. Plus this is fun if a little exhausting. Commissioning astronomical instruments has always been the most enjoyable part of my career in the past, and it's nice to get a chance to do something like that again.

As part of the preparations, UKIRT had to be converted back to Cassegrain mode for a couple of weeks and that involves a lot of night time calibration and testing work. On our first night after the conversion we did every measurement and calibration possible other than reshaping the primary mirror to take into account gravity. The latter takes several hours of observations and couldn't be done right at the start but despite that Jack (the telescope operator) and myself thought we'd have a quick test of the telescope by taking some infrared images of Pluto using a facility instrument called UFTI. I didn't expect much, after all the primary and secondary mirrors hadn't been calibrated, but we had a nice surprise!

In the top image, Pluto and its moon, Charon, are easily seen. Charon wasn't discovered until 1978 and even then the discovery was controversial. Ground-based telescopes are always subject to the effects of the atmosphere and until quite recently resolving Pluto and Charon was a very difficult task. Imagine my surprise when the automatic data reduction software spat out the image above (oh, OK, it didn't have the circle in it!). Remember, the telescope wasn't ready for this type of observation, I just wanted to see what image quality we had before working on the engineering models for the mirrors. I was also curious to see if we could figure out how to find Pluto in the first place!

The second image is actually two images combined. I wanted to make sure that we were actually looking at Pluto so we took another image a few minutes later; the idea being that the stars should stay in the same place but Pluto and Charon would have moved with respect to the background stars. They did and we could still see Charon.

OK, not as exciting as the most distant quasar ever seen, but given it's been nearly three years since we were last in this mode, the telescope had just been handed over by the engineers and I'd forgotten everything about running things in Cassegrain mode, I was rather impressed!

This is a close up of the K-band image of the Pluto-Charon system. The images are a little elongated but that's because we hadn't done the wavefront sensing at this point. For those who know a little about optics, there's some coma and astigmatism in the images which I hope are now removed after last night's engineering observations. For those that know little about astronomy, here's a little spiel I wrote for our staff:

Pluto, now classified as a dwarf planet, is approximately 2.9 billion miles away at the moment and it takes light over four hours to reach us from there, just to give you some idea of the scale of our Solar system. It's about a fifth the diameter of the Earth and its mass is only about a fifth of our own moon. Charon is only about 750 miles across and only about a fiftieth of the mass of our own moon.

Tomorrow night it's back to commissioning and engineering and after that hopefully some world-beating planetary science. And then maybe I can get some sleep...

1 comment:

Anonymous said...

Thanks for the info. My husband told me he thought Pluto was an ASTEROID as there was publicity a while ago that Pluto was not a planet. What will they think of next?