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Yale Astronomy

100 Earths Project

Why Search?

It is humbling to realize that humankind occupies a tiny pale blue dot in the unimaginably vast Universe and that we are recent newcomers to the Earth. We have learned that life on this planet began more than 3 billion years ago and that there have been millions of other species and at least five major mass extinctions. Yet, of all the species that have inhabited this planets, humans are the first to build telescopes to unravel the mysteries of the Universe. We are the first to understand that the Universe started with a Big Bang and that the atoms in our bodies were forged in the cores of stars. We search because we have insatiable curiosity, a desire for beauty and awe, and an incredible gift for creating the technology to explore the universe. We search because we need to know whether others are out there.

View from an 
Image by Haven Giguere

Why Earths?

Twenty years ago, we did not know if planets orbiting other stars ("exoplanets") were rare or common. The search for planets is a search for life elsewhere. We are searching for terrestrial worlds that might be laden with oceans of water, like our own planet. This may seem anthropocentric; however, we would have a hard time recognizing life that is fundamentally different from anything on Earth. A logical first step is to look for life as we know it: carbon-based life inhabiting the surfaces of rocky planets. We are surveying the closest stars because the signatures of life are likely to be subtle and will be even more difficult to detect around distant stars.

The search for 100 Earths in the solar neighborhood is a grand quest. Nothing quite like this has been done before. The detection of 100 Earths would provide a sample size that is large enough to place constraints on the occurrence of exobiology. This project will launch humankind's exploration of other worlds in our Galaxy.

Our experience designing and building the CHIRON spectrometer for planet hunting at Cerro Tololo Observatory in Chile has helped us to navigate the path forward. Our team at Yale takes a methodical and quantitative approach to developing instruments for planet searches. We have built an instrument "diagnostic facility" to test the impact of different design choices on stability and measurement precision.

Five Point Innovation


Building an instrument to detect Earths is incredibly challenging. Our detection technique makes use of a spectrometer, which allows us to measure the velocity tug that orbiting planets exert on their stars. We have 15 years of experience with this technique and we are developing the technical innovations required for the next breakthrough with EXPRES: the EXtreme PREcision Spectrometer, the instrument that we are designing to detect 100 Earths.

  • COUPLING OF LIGHT. Our team has pioneered instrument designs to couple light from the telescope into the instrument using specially fabricated optical fibers. The prototype instrument hs been designed and tested. Our team demonstrated a factor of 50 improvement in the illumination stability at the Keck Telescope in Hawai'i.
  • ENGINEERING. We are designing a vacuum enclosure for our instrument with extreme pressure, temperature and vibration control. This effort has stringent engineering requirements, but the scope of the effort is well understood and low risk.
  • DATA ANALYSIS. In a new joint venture with Applied Mathematics at Yale, we are developing new data analysis techniques, such as sharpening algorithms that employ wavelet analysis to model our data.
  • WAVELENGTH STABILITY. We are developing a next-generation wavelength calibrator that creates a regular pattern of emission lines, locked to a precise hyperfine laser line. This is a cutting-edge effort that is being pioneered in our lab.
  • UNDERSTANDING THE STELLAR NOISE. Our group has long been advocating for instruments that do more than measure stellar velocities with exquisite precision. We need to track, measure and decorrelate the stellar noise sources (not just average over noise sources). These more stringent requirements set the top level design specs for EXPRES.