HAT-p-7b confirmation and many great things to come – With Natalie Batalha
Exactly five months after the launch of the Kepler spacecraft, NASA will hold a press conference to present early science results. Early science results. I linger over those words with great pleasure. It isn’t sufficient to simply write about the science or even comment on the mood of the science team at Ames during the days when they examined that first data transmittal. I must rewind a bit, for there is a story here to be told.
In 1971, Rosenblatt published a paper in which he states that planets as small as Mars can be detected from small, ground-based telescopes using transit photometry. William (Bill) Borucki worked to reproduce Rosenblatt’s results. In 1984, he published a paper that differed on one important point – the size of the planets that could be detected from the ground. The Earth’s atmosphere, he argued, would prevent us from detecting anything much smaller than a gas giant. To detect terrestrial-sized planets, we would have to put our telescopes in space.
In the late 80’s/early 90’s, NASA created the Discovery Program for Solar System exploration. It issued its first Announcement of Opportunity sometime around 1992. This first AO requested proposals for concept studies. The program budget and objectives were a good fit to the science that Borucki wanted to do. He put together a team and submitted a proposal for a mission they called FRESIP: “FRequency of Earth-Sized Inner Planets.” It was rejected. The reason: no sufficiently sensitive detectors were believed to exist. In response, Borucki organized a workshop at NASA Ames, calling experts in the field to discuss what type of science could be done with a mission like FRESIP.
In 1994, the Discovery Program office issued an AO requesting proposals for its first full “Discovery-class” mission. Once again, Borucki’s team submitted a proposal to put a CCD photometer at one of the orbital lagrange points. The proposal was rejected. The reason: experience with the Hubble Space Telescope suggested that FRESIP would be too expensive for the Discovery Program – a program whose byline was “faster, better, cheaper.” The design would have to be revisited. In the meantime, the Ames team published a paper demonstrating, via laboratory experiments, that current CCD detector technology could indeed yield the precision required for the detection of a transit from a earth-like planet orbiting a sun-like star.
The next AO from the Discovery Program office was issued in 1996. This time, Carl Sagan, Jill Tarter, and Dave Koch put a little frosting on the cake they were trying to sell. They renamed the project. FRESIP became Kepler – a name destined to inspire and capture the imagination. The team paid special attention to the budget – providing three different cost estimates. A cheaper solar orbit was identified, and the CCD detectors were proven capable. But again, the mission was rejected. The reason: no one had ever done automated photometry of tens of thousands of stars simultaneously. Could it be done? Borucki would try.
In 1997, the Vulcan project was born. Lick Observatory allowed Borucki to use one of the old abandoned domes up on the mountain – the Crocker dome. He hired engineers to fix the dome and its motors. He found an old lens and borrowed a CCD detector. Ames machinists built a pier for the telescope mount. The money initially came from discretionary funds. Borucki made a bit of a pest of himself by often asking Ames management for dribbles of money. The entire observatory was built on a shoestring budget. Necessity was the mother of invention. A rain shield was rigged with pulleys above the telescope to protect it from the leaks in the rusty dome. A Teflon paint bucket became the housing of the calibration lamp. Who knew that Teflon would be such a good light diffuser? With time, the little observatory became a fully robotic facility tied to a weather station that fed it the information it needed to decide if it was safe to open up and take pictures of the sky. Vulcan served as Borucki’s training wheels. The team did automated photometry of tens of thousands of stars simultaneously.
The next Discovery Program AO came out in 1998, continuing its two-year cycle. Once again, the team submitted a proposal. This time, the review panel conceded that the detectors could achieve the requisite precision and that automated photometry could be done on such large numbers of stars. But once again, the proposal was rejected. The reason: the team did not demonstrate that it could manage all of the potential on-orbit noise sources, such as telescope jitter. However, the proposal was compelling enough that NASA gave the team a bit of seed money in order to build a laboratory experiment to test the effect of the spacecraft environment on photometry.
Dave Koch – the Deputy PI – led the effort to create the Kepler Tech Demo. In record time, a telescope was built – one that would never actually point at the open sky. To simulate stars and the signal of a planet transiting a star, Koch had laser holes drilled into a metal plate that would be illuminated from behind by a uniform, constant light source. He then laid very fine wires over the laser holes. Putting one-thousandth of an Amp of current through the wire caused it to expand just enough that it blocked out the same amount of light coming through the hole that an Earth-like planet would block passing in front of its Sun. With well-built hardware and well-designed software, the team showed that it could “find” the transit events even under the conditions it expected to face in space. Let’s see what else the Discovery review team could come up with!
In 2000, the next AO came out. For the FIFTH time, the team submitted a proposal. The team met with more luck this time. They were one of three teams invited in 2001 to submit a more thorough proposal containing more detailed design specifications. Finally, in December of 2002, Kepler was selected as Discovery Mission #10 (and would ultimately launch as the 11th). Success came 21 years after Rosenblatt first presented the idea of transit photometry and 18 years after Borucki first put forth the idea of a space-based mission to detect earth-like planets. Success came after 10 years of refining and improving the original proposal.
By this time, I had worked with Bill long enough to know a bit about his personality. I had observed the struggle. I had heard the murmurings of criticism about a project that few besides the core team sincerely believed in. What left the biggest impression on me was Bill’s constantly positive attitude in the face of rejection and criticism – his staunch resolve to never take criticism personally but rather to use it as a means of improvement — and his unwavering persistence.
During the development phase of the mission, I read the biographies of the man, Kepler. At a young age, Kepler was deeply impressed by the realization that the universe can be understood by geometry and mathematics. The mysteries of the Universe are there for us to discover, and they will be told to us in the language of mathematics. This idea held tremendous significance for him – “magnificent order” he called it. As a young, newly appointed professor of mathematics, he happened upon an idea as he was teaching in the classroom – an idea that would ultimately lead him to formulate his empirical laws of planetary motion. And while I was already intimately familiar with Kepler’s scientific body of work, I was completely ignorant of the arduous path that led him to those discoveries.
It took a full fourteen years for the seed to reach fruition – fourteen years to take an idea and turn it into an elegant empirical law of nature. The time was spent going forward, backward and around in circles. There was suffering and meditation, frustration and excitement, inspiration and agony, but never utter defeat. The obstacles were numerous – political, financial, personal, and intellectual – but never insurmountable. In reading the story, I gained a deeper appreciation for the journey itself and realized that great accomplishments all share this common thread – the unequivocal belief that the goal is attainable. I couldn’t help but fast forward to the story that was unfolding in front of me. Greatness is all around us and within us, and the lessons to be learned are the same. I am honored to be a part of such a worthy journey.
This year marks the 400th anniversary of the publication of Astronomia Nova in which Kepler presents his first two laws of planetary motion – a work so tremendously important that it is honored 400 years later as the cornerstone of modern astronomy. How fortuitous that our own Kepler spacecraft launched this year and is now returning its early science results!
At the end of the commissioning period, the science team took a 10-day set of engineering measurements and turned them into 480 relative brightness measurements of approximately 52,000 stars. Ordering each of these brightness measurements in a time sequence produces what we call a “light curve.” Looking at the first light curves was thrilling. We grabbed an encyclopedia of variable stars in an attempt to attach names to different types of stars, but we quickly realized that there were no names yet for many of the types of light curves we were seeing. It was difficult to adjust our perception to the spacecraft data after having spent years, even decades, looking at data from ground-based telescopes. Many of the light curves looked like they were drawn with a fine-point marker. I sent a sample light curve to a colleague and he replied asking me to please send the raw data as opposed to the “smoothed” data that hides the noise. It was a pleasure to tell him that this WAS the raw data.
One of the first things the team did was look at the light curves of the known transiting planets in the Kepler field. Gorgeous! Immediately, we saw the occultation of HAT-p-7b. No need for any complicated number-crunching to pull out the signal. There it was. You could see it clearly by eye. And then we realized that the size of the signal we were seeing is comparable to the size of the signal expected by an earth-like planet transiting a sun-like star. The secondary transit of HAT-p-7b demonstrates that the instruments and software are capable to finding a habitable world!! — the proverbial “proof of the pudding.”
Another milestone has been reached, and the team is full of optimism that the spacecraft will continue to “see” as keenly as it does right now. “Early science results.” I linger over those words with great pleasure and enjoy the anticipation of many great things to come.