Kepler: An Evolution and a Shift

The announcement by Kepler a little more than two weeks ago was undoubtedly huge. The discovery and confirmation of a really interesting planetary system consisting of six confirmed planets was released. This announcement was coupled with the discovery of over 1200 other planet candidates. In the time since the announcement, I have been struggling to fully comprehend the immense size of the numbers. Now, I have started to just realize that the numbers may not be the most interesting idea to keep in mind. We also have to step back from the recent news and see that the Kepler announcement may be the representation of the start of a new era and a giant shift in looking for life outside of the Earth.

At one level this Kepler announcement represents the evolution of our exoplanet detecting skills, and the number of planets discovered does tell a huge story. The rapid pace we have achieved in detecting exoplanets is no small feat. About 15 years ago, the first extrasolar planets, about the size of Jupiter, were just beginning to be detected. Before these discoveries, many scientists doubted ever being able to detect an extrasolar planet. Now, including great contributions being made by the Kepler spacecraft, we may have about 1500 planets detected and confirmed soon, a remarkable jump especially since many of these planets are much smaller than Jupiter. The Kepler announcement is also encouraging in that its discoveries are only being made in a single patch of sky. This area covers only about 1/400 of the area of the entire sky. Admittedly, other patches of the sky may not be as rich of stars containing planets as Kepler’s field of view, but it is extremely likely a huge amount of planets are still waiting to be discovered.

What really excites me though is that this announcement marks a shift in our search for extraterrestrial life. Although Kepler’s mission is to look for planets and not life, I feel that  the scientific community and the rest of society is particularly interested in exoplanets because they may offer clues as to whether Earth life is an anomaly or the norm. This is why in every news piece I have read about the announcement so far, the fact about the list of potential Kepler candidates containing 54 planets about the size of the Earth located in the habitable zone is particularly emphasized. Any of these planets could contain life that is similar to ours and therefore their discovery captures our attention. The Kepler mission in particular represents a new era, in which our search for life outside our solar system is passing from a passive approach to a more active approach. In the era before Kepler, finding life outside of the solar system meant relying on projects such as SETI (Search for ExtraTerrestrial Intelligence). SETI attempts to detect signals that intelligent life may be broadcasting. This relies on the lifeforms having evolved and progressed as a society far enough so that they are able to regularly broadcast signals in the specific frequency ranges that Kepler is able to detect. Kepler, on the other hand, is taking a more active role. Kepler actually searches for planets that may be hospitable to life. Afterwards these planets can be examined in detail for traces of life, which do not necessarily have to be left behind by intelligent life.

The change, I think, is extremely important. Our search for life has become much more efficient and likely more fruitful. It as if we no longer have to face an expansive ocean hoping intensely that something in it will make contact with us. We can now wade in, start turning over rocks, and examine what we find. This is why I have been very obsessed and excited about the announcement. I believe when looking back after a number of years, the Kepler project and announcements like this will mark the point in history when we no longer sat back, but stood up and got our feet wet.

Kepler Discovers New Planetary System and Announces Over 1200 Planet Candidates

The Kepler spacecraft started doing its work in May 2009, continuously watching the stars contained in a patch of sky with the hope of being able to discover exoplanets. Just recently, the Kepler team had a very exciting set of announcements resulting from this diligent work.

An artist’s conception of the Kepler-11 system.
Image: NASA/Tim Pyle

Comparison of Kepler-11 orbit sizes
and our Solar System’s orbit sizes.
Image: NASA/Tim Pyle

One of these was the discovery and confirmation of a newly found planetary system with six confirmed planets. Their star, Kepler-11, is a sun-like star, located about 2000 light years away from Earth. This star is only the second known so far to host multiple planets outside of our solar system, and now holds the record for hosting the most known planets. Plus, all of its planets have extremely tight orbits. The largest orbit is smaller than that of Venus in our solar system, while the other five orbits are even smaller than that of Mercury. This results in the most compact planetary system yet discovered in addition to the largest planetary system by number. Furthermore, the planets are bigger than the Earth, with the largest planet comparable to the size of Uranus and Neptune in our solar system. Still five of the six newfound planets are among the eight smallest extrasolar planets found so far. These interesting facts and characteristics of the system also lead to some clues about the formation and the dynamics of the system.

Kepler detects planets by measuring for drops in the light of their stars as they pass across, called the transit method (This method is detailed further in this previous post about Kepler). Measuring the changes in how much the light drops, at what times, and in what patterns can allow astronomers to calculate characteristics of the planet like size, distance from the star, and number of planets. Since the planets are located extremely close to each other in this particular system, five of the six planets produce significant perturbations on each others orbits that are measurable by Kepler. As they are detected, they will let the researchers calculate estimates for the masses of these planets. Further transits in the future will allow the estimates to be further refined. Adding this information with the sizes of the planets leads to the density of the planets that in turn could allow other researchers to hypothesize about the makeup of the planet. The densities of the planets in the Kepler-11 system appear low, suggesting that they are gaseous planets composed of light elements. These would be similar to planets like Neptune in our solar system rather than terrestrial planets like Earth. The conclusions also give suggestions about the formation of the planetary system. Presence of a large amount of light gas likely means that these planets were formed early in the history of their system. Finding out more about the formation of other planetary systems, such as this one, could, in turn, lead to valuable realizations about our own system.

Locations of Planet Candidates in Kepler FOV
Image: NASA/Wendy Stenzel

Yet, probably the more important announcement could be that in addition to these confirmed planets, Kepler has found over 1200 other planet candidates. These are discoveries that result in data that may be similar to that produced by the presence of an exoplanet, but needs to be verified and confirmed. The amount of actual planets from the list will almost definitely be less, but, more importantly, by how much? Some analyses are suggesting that about 80 to 90 percent of the objects on this preliminary list could be planets. This means that the amount of exoplanets discovered (currently about 530) could go up very significantly, by around 1000 (or about 200% of the current number) if the early analyses end up being accurate. Plus, in that preliminary list of planets, 54 are located in the habitable zone of their stars. This zone includes the orbits where a planet could potentially hold liquid water. The radius of one of these is about 0.9 times the size of the Earth’s, while the radii of four others are less than two Earth radii. A planet more Earth-like than any discovered so far may be among these data.

Results like this one are hugely important. They suggest the presence of the hundreds of other star systems, some unique systems like Kepler-11, or perhaps others also like our own solar system.