Three hundred seventy-nine years ago, the famed astronomer Galileo Galilei went on trial. Today, it’s Kepler’s turn. And I don’t mean Johannes Kepler; I mean the eponymous NASA spacecraft. While Galileo was on trial for saying that the Earth went around the sun, which was heresy in Rome in 1633, the Kepler Mission is on trial for nothing more than the common inquisition of our time. The government must decide whether the Kepler Mission deserves a share of the scant funding available for space missions in this bruised economy.
The Kepler Mission, which detects transiting exoplanets, is coming to the end of its nominal three-year mission. Today, several Co-Investigators (Kepler Mission leaders) will propose to Congress to extend the mission at the NASA Astrophysics Senior Review. If Kepler does not obtain additional financial support, it will “close its eyes forever,” in the words of Co-Investigator Natalie Batalha in the First Kepler Science Conference last December.
Why should we extend the Kepler Mission?
The new catalog release introduces 1091 new candidates, bringing the total number of planet candidates to 2,321. These new planets are, on average, smaller and colder than the planets yet discovered, indicating that Kepler is on the verge of detecting true Earth-size planets in the habitable zone. To quote the new catalog of Batalha et al.,
“The progression toward smaller planets at longer orbital periods with each new catalog release suggests that Earth-size planets in the Habitable Zone are forthcoming if, indeed, such planets are abundant.”
If Kepler does not obtain additional financial support, it will “close its eyes forever.” – Natalie Batalha.
But what if small planets are not abundant? Bear in mind that the number of planets increases for smaller planets at larger orbital distances, implying small planets should be very abundant! Kepler just needs more time to find them.
Extending the mission will grant Kepler the opportunity to achieve the mission objective: finding the frequency of true Earth analogs (Earth-size planets at orbital periods of one year).
Wasn’t Kepler supposed to have found the Earth analogs by now?
Yes, it was. However, when the mission was initially designed, no one knew what the typical change in brightness for a star on very short timescales (or “jitter”) was. The jitter is important because it introduces noise to the stellar light curve, which makes it more difficult to detect a planetary transit of a particular depth. When the Kepler team designed the mission, they only knew the jitter of the sun, which is 20 parts per million, and so they used this as an estimate of typical stellar jitter. However, Kepler has since shown that most stars have a jitter of 30 parts per million. This additional noise in the light curve increases the number of transits required to detect a transit of a given depth. To see more transits of a particular planet, we need more time. That’s why Kepler needs an extended mission to achieve its mission goal.
But Kepler has still done a lot of cool stuff, right?
Absolutely! Here are some treasures Astrobites has written about:
- Observing star spots
- An evaporating planet
- Circumbinary planets (here and here)
- Looking for exomoons
- Letting the public find planets (here and here)
- A miniature solar system with Earth-size planets
- Asteroseismology (here and here)
- A planet discovered by transit timing varations
- Statistical analysis of planet densities
- The first rocky exoplanet
- The first super-Earth in the habitable zone
Are there any reasons against extending the Kepler Mission?
This is an important question to ask, and the review panel might ask this of the Kepler team. Like many high-quality things, Kepler is expensive. The personnel and large computing power required to run and improve the pipeline (without which data processing would be practically impossible), the high bandwidth required to download large volumes of data from this distant spacecraft, and other operational costs make Kepler more expensive – requiring a hundred million dollars over the next five years – than many other major telescope missions, including the Spitzer and Hubble Space Telescopes.
Yet, Kepler is revolutionizing science. Three hundred seventy-nine years since Galileo went on trial for believing the Earth went around the sun, we still commend his courage in challenging widely held beliefs in order to promote real understanding of the Solar System and our place in the universe. Kepler has staggered the world with its riches of planets: diverse star systems with multiple planets, miniature solar systems, super-Earths, rocky worlds, habitable worlds, and, hopefully soon, an Earth analog. Tell me this does not revolutionize our understanding of Earth, the Solar System, and our place in the universe. Tell me these are not riches. Tell me that the Kepler Mission does not deserve to keep its eyes open.