Scientists Accurately Quantify Dust Around Planets in Search for Life

W. M. Keck Observatory press release

A new study from the Keck Interferometer, a former NASA project that combined the power of the twin W. M. Keck Observatory telescopes atop Mauna Kea, Hawaii, has brought exciting news to planet hunters. After surveying nearly 50 stars from 2008 to 2011, scientists have been able to determine with remarkable precision how much dust is around distant stars – a big step closer into finding planets than might harbor life. The discovery is being published in the Astrophysical Journal online, on December 8th.

A dusty planetary system (left) is compared to another system with little dust in this artist's conception. Credit NASA/JPL-Caltech
A dusty planetary system (left) is compared to another system with little dust in this artist’s conception. Credit NASA/JPL-Caltech
“This was really a mathematical tour de force,” said Peter Wizinowich, Interferometer Project Manager for Keck Observatory. “This team did something that we seldom see in terms of using all the available statistical techniques to evaluate the combined data set. They were able to dramatically reduce all the error bars, by a factor of 10, to really understand the amount of dust around these systems.”

The Keck Interferometer was built to seek out this dust, and to ultimately help select targets for future NASA Earth-like planet-finding missions.

Like planets, dust near a star is hard to see. Interferometry is a high-resolution imaging technique that can be used to block out a star’s light, making the region easier to observe. Light waves from the precise location of a star, collected separately by the twin 10-meter Keck Observatory telescopes, are combined and canceled out in a process called nulling.

“If you don’t turn off the star, you are blinded and can’t see dust or planets,” said co-author Rafael Millan-Gabet of NASA’s exoplanet Science Institute at the California Institute of Technology in Pasadena, California, who led the Keck Interferometer’s science operations system.

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Working Together One Last Time

You could always tell when the interferometer was on-sky. Both telescopes would be pointed at the same object, both domes open to the same direction. Any other time you will find each Keck telescope doing its own thing. With the interferometer shut down, it will be an odd night indeed when the telescopes are pointed in the same direction.

The Last Interferometer Run
Both Keck telescopes observing the same object during the last night of interferometer observing.

The Last Interferometer Run

Tomorrow morning I will begin to power down the systems. One by one I will open the switches on gear that has rarely been powered off in years. In a matter of minutes it will be off. Dozens of computers, servo drives, camera controllers, racks of gear, silent and dark. I will also shut off the liquid nitrogen to each camera in turn. This will take a bit longer, a couple weeks will be needed to properly warm and back-fill each camera with dry nitrogen for storage. Meanwhile, Brett will carefully cover each optical surface in optical cloth and plastic. A few bits of gear installed in the telescope will be removed to be stored in the basement. By the end of August the Keck Interferometer will be mothballed.

This is the last run, three nights of observations. Two of those are behind us, the third beginning, the end is rapidly approaching.

FATCAT Dichroics
The FATCAT dichroic beamsplitters in the Keck interferometer beam lab
I look about at all of the gear and consider the thousands upon thousands of hours it took to assemble, test and troubleshoot this complex scientific instrument. Years of work by so many people. I look about the control room at the racks of equipment, the masses of cabling, the physical results of so much effort. The non-physical likewise represents a staggering amount of work, the software that allows the entire system to operate. My own contribution seems insignificant. Here and there I note pieces of gear I installed, cables run, cards I have modified, and some many parts of the system that I have had to repair across the years. The sense of loss at shutting this system down is overwhelming.

The plan is to carefully mothball the interferometer in place, in such a way as it could be reactivated with a few weeks of work. Maybe, some source of funding might allow the instrument to be used again, that is the hope. But we know how difficult the current budget environment has become.

Fast Delay Lines
The Keck Interferometer beam expanders and fast delay lines
Still, we are going out in style. This last run has attempted what has never been tried before… We are using AO lasers on both telescopes to reach targets never reachable before. The newly commissioned Keck 1 laser capability making this possible. We have successfully gathered data using the dual laser AO mode, a real first.

Oddly, one of our laser spotters did not make it to the summit and I was obliged to fill in. Fortunately it was a lovely night on the summit, not very cold and with no wind to make it miserable. For a couple hours I relaxed in the Laser Suzan chair, watching the sky. Above me arched the Milky Way, somewhat dimmed by a bright Moon, but still beautiful. A few bright meteors punctuated the night. The scene was a made a bit surreal by three lasers, all targeting the galactic core, the very center of our galaxy. Beside me the camera regularly issued the soft sound of the shutter, taking images of the night.

The second night was a series of galactic targets and a couple AGN’s. The final analysis will take time, but initial indications are that we have good data on at least some of the targets. A couple targets proved too faint for the system to track on. No surprise, we planned to reach a little with this last run.

Thus we begin this last night, the practiced evening routine is complete, final checks done. The last targets a list of selected YSO’s (young stellar objects) to be observed in L-Band. We settle in for the night, hopefully a quiet night. As usual, if I am busy, things are not good. All is going well, a fitting end to the instrument and a testament to all those who have put so much into the system. Something to remember.

An Interesting Day

Any day that starts with two flat tires is bound to be an interesting day.

Waiting for a Spare
Waiting for another spare tire to fix the second flat on Mauna Kea
Yes, not one, but two flat tires in a matter on moments. I felt the first tire blow out and as we inspected the damage a hissing could be heard from the opposite side. The summit road is known to be a problem, and flat tires are not an uncommon event. We do get practice changing tires on this road. Fortunately other Keck vehicles were coming up behind us, and we could ask for another spare to be brought down from the summit. In the meantime we spent a pleasant half hour waiting for the second spare. The weather was beautiful, and so was the view from high on the side of Mauna Kea.

I had planned on working on one of the cameras in Interferometry. The camera has been having trouble automatically filling with liquid nitrogen. In addition I had a list of smaller issues that needed to be dealt with. Unfortunately one of those minor issues turned out to be not so minor.

Fast Delay Lines
The Keck-Keck Interferometer fast delay lines
Thus I spent much of the day troubleshooting Fast Delay Line #5. Used to compensate the optical path between the two telescopes, the delay line is a cart that runs on rails, carrying a set of mirrors. The cart should track very smoothly, changing the path length on the order of micrometers (a few ten thousandths of an inch), instead it visibly jittered and jumped along the rail, something wrong in the motor control software or circuitry. It took much of the day, but in the end it was tracking smoothly.

The entire day was busy from beginning to end. I attempted to finish the last few tasks on my list as the last few minutes of the day sped away. The rest of the guys were ready to leave about a quarter to five, while I was still connecting a few last metrology cables. “Yes, I am coming!” I answered on the radio for the second time. I grabbed my tool bag and headed to the door as the clock hit 17:00.

One of those days I return home exhausted. I will have to head up again, quite soon, to deal with other problems still unfinished. Hopefully a somewhat less complicated day.