Keck Planet Finder: Earth-like planet with sun and other planets in the distance.

terrestrial sky | Keck Planet Finder starts searching for other earths

View larger. | Artist’s concept of Kepler-186f, a rocky exoplanet about the size of Earth and potentially habitable. It is about 500 light years from Earth. The Keck Planet Finder will search for such rocky exoplanets. Image via NASA Ames/SETI Institute/JPL-Caltech/Sci.News.

Astronomers have so far discovered several thousand exoplanets. They are worlds orbiting distant suns, and range in size from some larger than Jupiter to small rocky planets like Earth. The rocky planets are most likely habitable. But small rocky planets are difficult to spot. And now there’s a new tool to help you find more of them. Astronomers at the WM Keck Observatory in Hawaii announced the Keck Planet Finder on November 10, 2022, saying it had just reached first light.

These scientists said the Keck Planet Finder is the world’s most advanced high-resolution visible-wavelength spectrometer. Its purpose is to search for smaller planets like Earth orbiting other stars, particularly those in the habitable zone.

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Keck Planet Finder begins its mission

With First Light – the first time a telescope or telescope instrument open his eyes – achieved, Keck Planet Finder can now begin its mission to find other Earth-sized or even Earth-like planets. As Hilton Lewis, director of the Keck Observatory, said:

The advent of KPF marks a major and exciting step forward in our ability to advance the search to eventually find habitable Earth-like planets around other stars. We have been waiting for the arrival of KPF for almost a decade and are excited to take our already highly successful exoplanet discovery program to the next level.

Andrew Howard, Caltech’s KPF Principal Investigator, added:

Seeing the first astronomical spectrum from KPF was a moving experience. I look forward to using the instrument to study the wide variety of exoplanets and to unravel the mysteries of their formation and evolution to their current state.

First light for Keck Planet Finder: Jupiter and 51 Pegasi

Keck Planet Finder’s initial goals for First Light included a planet much closer to home and a distant star. The astronomers made these first observations – of Jupiter and the star 51 Pegasi – on November 9th. The instrument successfully captured the light spectrum of both objects for its initial testing. In fact, the planet 51 Pegasi b, orbiting the star 51 Pegasi, was the first exoplanet found to be orbiting a Sun-like star using the Doppler technique (or Doppler spectroscopy).

Now Keck Planet Finder is ready to begin its mission to search for other potentially habitable planets similar to Earth. We’re ready to learn more about planets around other stars that are relatively close to us for the first time. As noted by Sherry Yeh, associate instrument scientist at Keck Planet Finder:

Before the recent boom in exoplanet discovery over the past two decades, we didn’t really know what other planets were out there. We didn’t know if our own solar system or our own earth was common. We are the first generation that will truly understand other planets in our galactic neighborhood.

The technical doppler

So how will Keck Planet Finder actually find planets? The Doppler technique is used for this. In fact, the Keck Observatory was the first to develop this method. It detects planets by looking for the gravitational effects they have on their stars. In other words, it looks like the stars can be seen flutter easy. A planet’s gravity causes this wobble and affects – very slightly – the motion of the star.

Of course, more massive planets with higher gravity are easier to spot than smaller rocky planets. This is where Kepler Planet Finder comes into play. In fact, it’s strong enough to see extremely small fluctuations—up to 30 centimeters/second—like small planets. That’s slower than a human walking. For comparison, the Keck Observatory’s current planet-finding instrument, called the High-Resolution Echelle Spectrometer (HIRES), can detect stellar motion of 200 centimeters/second. In contrast, Keck Planet Finder is much more sensitive, just what is needed to search for Earth-sized planets.

Josh Walawender, instrument scientist for Keck Planet Finder at Keck Observatory said:

Just a few decades ago, the challenges of such measurements were considered insurmountable. SPF is the result of a prodigious amount of human ingenuity expended to solve problems and circumvent obstacles to our understanding of the universe around us. To me, KPF represents one of the best qualities of humanity: the humble desire to see and learn about the universe around us, and thus better understand the place in which we live.


How can Keck Planet Finder achieve such accuracy? The answer lies in the special material the spectrometer is made of. This material, called Zerodur, is a glass-ceramic hybrid. It is able to maintain its shape despite temperature changes. This ability is essential as even minute movements of the Keck Planet Finder instrument can result in false alarms. In other words, show Doppler shifts in stars that aren’t actually there. Caltech’s Ryan Rubenzahl explained:

Light bounces between mirrors inside the instrument. As the spectrograph’s base expands, the distance between the mirrors changes, causing light to land in the wrong place. It may appear as if the starlight has Doppler shifts due to orbiting planets, but in fact the instrument itself has shifted.

In addition, the main mirror segments of the Keck observatory are made of the same material.

Keck Planet Finder is the first spectrometer of its kind to use Zerodur. Howard said:

This is the first spectrometer that Zerodur integrates into its design. The material, which comes in huge slabs, is very fragile and difficult to work with, but that’s what makes KPF so sensitive to smaller planets.

2 white telescopic domes with rocky area in foreground.
View larger. | These are the twin telescopes at the WM Keck Observatory in Hawaii. Image via T. Wynne/ NASA/ JPL/ Wikipedia (Public Domain).

Planets in the habitable zone

Keck Planet Finder can not only find smaller rocky planets, but also those in the habitable zones of their stars. For now, it’s confined to smaller, cooler stars like red dwarfs. But red dwarfs also have habitable zones, and astronomers have already found many planets orbiting them. As Howard: explained

Stars cooler than our Sun have habitable zones closer to the star. All of the Earth-like planets in this zone would huddle close to their stars like a campfire. We will continue to tune and refine KPF to detect even fainter wobbles, with the goal of eventually having the sensitivity to detect Earth-mass planets orbiting stars like our Sun, the true analogues of Earth.

Keck Planet Finder can also determine the composition of about 1,000 planets previously discovered by NASA’s Kepler space telescope. Howard added:

KPF will be much more precise than our current tools and allow for richer science through better measurements of the smaller planets’ masses, orbits, and compositions. It will also be faster, allowing us to measure planetary masses in much less time than before. That means we can measure more planets.

Keck Planet Finder will officially start planet hunting next spring.

Conclusion: The Keck Planet Finder instrument on the Keck 1 telescope in Hawaii has reached first light. It will now start searching for habitable Earth-sized planets around other stars.

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