Astronomers have found the shattered remains of an asteroid that contained huge amounts of water orbiting an exhausted star, or white dwarf. This suggests that the star GD 61 and its planetary system – located about 150 light years away and at the end of its life – had the potential to contain Earth-like exoplanets.
The new research findings used data collected from NASA’s Hubble Space Telescope, both of W. M. Keck Observatory’s Keck I and Keck II telescopes, as well NASA’s FUSE telescope, and are reported today in the journal Science.
Artist impression of a rocky and water-rich asteroid being torn apart by the strong gravity of the white dwarf star GD 61. Credit: Copyright Mark A. Garlick, space-art.co.uk, University of Warwick and University of Cambridge.This is the first time both water and a rocky surface – two key ingredients for habitable planets – have been found together beyond our solar system.
Earth is essentially a “dry” planet, with only 0.02% of its mass as surface water, meaning oceans came long after it had formed; most likely when water-rich asteroids in the solar system crashed into our planet.
The asteroid analyzed is composed of 26% water mass, very similar to Ceres, the largest asteroid in the main belt of our solar system. Both are vastly more water-rich compared with Earth.
The new discovery shows the same water delivery system could have occurred in this distant, dying star’s solar system – as latest evidence points to it containing a similar type of water-rich asteroid that would have first brought water to Earth.
Astronomers at the Universities of Cambridge and Warwick say this is the first “reliable evidence” for water-rich, rocky planetary material in any extrasolar planetary system.
Keck tracks every night with a custom, in-house database. These form a complete log of what occurred every night… The routine, the problems, the small disasters of operating a complex facility on top of a mountain. Reading these logs every morning is a ritual for many of the staff. A synopsis arrives in our e-mail each day, to be read on an iPad over breakfast, or as soon as you sit down at your desk.
The Keck 1 telescope operator’s consoles in the night during laser AO observingFor many in the operations department the contents of the logs set the pattern of the day. Was this a quiet night with no issues? Or is this a day when you need to drop everything to address some serious problem on the mountain?
Below is a typical night log from a quiet night. Reading through the logs each morning reveals much about the inner workings of the observatory. Who was working the night, the visiting astronomers and their subject of study. The logs also contain a number of statistics that are used to monitor the performance of the observatory.
An evening stop in the local market to pick up a few groceries. There is always a stack of local newspapers on the checkout counter. But this edition looked a little familiar… That is my photo! I knew Steve, our PIO at Keck, had forwarded the image to the newspaper. I did not expect it to be at the top of the front page!
The image has gotten some traffic. Posted to Facebook the news of snow on Mauna Kea resulted in the highest traffic day I have had in years for this blog. It is not even a great image, just a snapshot taken as we headed for the vehicles to get off the mountain. The light is horrible, the scene seems flat, but it is snow, and that is always big news around here.
Actually, this is my second front page image. A panorama shot from the Keck roof was featured on the front page of the Star-Advertiser earlier this year. It is always a nice surprise to see an image of mine get some press!
The front page of the West Hawaii Today, 12 Oct 2013
Winter might just be starting in Hawai’i. A fall storm dropped the season’s first snow on the summit of Mauna Kea this afternoon. Not much, just enough to turn the summit white. I had to scrape the frozen snow from the windshield to free the wipers before I could drive down.
We got 1.2″ of rain at the house, quite a bit when you consider we get 10″ a year in the shadow of the mountain. I am headed back to the summit tomorrow morning, wondering what we will find, this storm is just starting.
A light snowfall marks the start of winter on Mauna Kea.
Warping is not much fun. Warping is now on my list of responsibilities. At least I know I am accomplishing something critical to the operation of the telescope.
A Keck mirror segment after stripping and cleaning, ready to place in the chamber to receive a new reflective coatingWarping is a process of tuning the performance of a mirror segment after a segment exchange. A segmented mirror offers large advantages over a monolithic mirror, not least of which is the ability to swap a few segments out for re-coating and refurbishment without the weeks of downtime needed to re-coat a monolithic mirror. Throughout the summer Keck schedules a couple days of SegEx each month, so that at the end of the summer we have a completely clean and re-coated mirror.
Exchanging segments does require some interesting procedures to realign each new segment, each must be warped and the edge sensors tuned. The first few hours of the night after a SegEx is used to evaluate the performance of the newly replaced segments. Using a special alignment camera system the optical figure of each segment can be evaluated and a set of corrections generated to be applied the next day… Warping.
A map of the segment types in the Keck primary mirrorThere are six segment types that make up the primary mirror, each with the slightly different curve needed to make up the correct part of the hyperbolic curve. In theory the segments are interchangeable, any type four can be swapped with any other type four. This works… With a little help. It is necessary to adjust the figure of each segment, just slightly, to tune the figure of each segment for its place in the array.
To apply the correct pressure there are small knobs and screws at specific points in the whiffle tree. Each adjustment point also contains a strain gauge, allowing the applied pressure to be measured precisely. A computer and analog interface allows all of the points to be read out and checked against the calculated values.
the warping computer set up in the subcellThere are thirty adjusters and strain gauges on the back of each mirror segment. The problem is that you can not simply adjust each one. Adjustment of one point affects all of the nearby points, particularly if the adjustment is large. Typically it is necessary to go around three times before the segment is properly warped. Thirty adjustments becomes ninety. Three segments in a day becomes 270 knobs to turn, 540 over two days, a lot of knobs.
After setup, it takes about an hour to do each segment, an hour of painstaking frustration. the mirror cell is just the right height, too high to sit down and reach the knobs, too low to stand up fully. Working in a jungle gym of frigid steel just makes it worse. A day in the mirror cell is a nice recipe for a tired and sore body.
How careful was I? Did I get all of the points set correctly? The computer is displaying all of the correct numbers. I will not know until the next day, when the night’s performance data is reduced, when we can see the figure of the primary mirror and check the errors.
My first warp is a success, most of the segments show less than 20nm rms error. Next SegEx there are only two segments being exchanged, but Sergey is threatening to have two others re-warped to address some lingering issues. Four? Better than six. Only 360 adjustments to make, more or less.
Today Mercury reaches maximum elongation, the furthest point it will reach from the Sun in our sky and the highest it will be above the sunset for this evening apparition. The planet is easily visible as a bright, starlike object about 25° above the setting Sun as twilight begins. Over the next couple weeks Mercury will slide back into the sunset, heading for inferior conjunction on November 1st.
