How many worlds are in that field of view, waiting to be discovered? We'll get a better idea soon. TESS measures starlight over long periods of time. When planets pass in front of their host stars, there's a slight drop in starlight. In the field of exoplanet science, this technique is called the transit method, and it tells us planet diameter, but not much else. In order to verify there's actually a planet present, we need follow-up measurements. That's why the Kepler space telescope differentiates between candidate exoplanets and confirmed exoplanets; the "candidates" are waiting on additional verification.

Additional verification is usually done with ground-based telescopes, using a technique called the radial velocity method. Orbiting exoplanets makes their stars wobble ever so slightly, and tracking those wobbles not only confirms there's a planet present, it also reveals the mass of the planet. When you combine this with the size information from the transit method, you can calculate density. And then, you can figure out whether your exoplanet is rocky like Earth, or gassy like Jupiter.

NASA's astrophysics division has a policy when it comes to ground-based observations: it doesn't do them. Traditionally, it's been the job of the worldwide science community to follow-up on discoveries made by space telescopes like Kepler and TESS.

That's about to change. In a first-of-its-kind partnership, NASA is teaming up with the National Science Foundation to work around its own rule. NASA still won't be directly funding observations; instead, it is paying for a new science instrument to be installed on a 24-year-old telescope at Kitt Peak National Observatory in Southern Arizona. The instrument will be one of the most sensitive of its kind, giving scientists a dedicated facility where they can take a closer look at the thousands of new worlds discovered by Kepler and TESS.

"To see"

The NASA-funded instrument is called NEID, which comes from the Tohono O'odham word meaning "to see." (Kitt Peak is located on Tohono O'odham land.) NEID is also a nested acronym for "NN-EXPLORE Exoplanet Investigations with Doppler spectroscopy." (I'll unpack NN-EXPLORE in a bit.) The instrument is being built by Penn State University.

NEID is a super-high-precision spectrograph that splits starlight into its component wavelengths the way a prism creates a rainbow. When an exoplanet wobbles its host star, the star spectrum wobbles, too. Scientists watch how that spectrum shifts over time to determine an exoplanet's mass.

NEID is being installed on Kitt Peak's 3.5-meter WIYN telescope. Jayadev Rajagopal, WIYN's telescope scientist and head of operations, told me NASA's original goal was for the spectrograph to detect star wobbles as small as 10 centimeters per second.

"That's like the speed of a tortoise," he said. No spectrograph has yet been able to reach such extreme precision. In recent years, instruments like European Southern Observatory's HARPS have crossed the one-meter threshold, after years of refinements. Rajagopal said the current record is about 75 centimeters. The final baseline for NEID will be 50 centimeters per second, with a goal to improve that over time.

Such extreme precision requires a very stable operating environment, year after year. A single point of starlight hitting the WIYN mirror gets shunted into a fiber-optic cable, which carries the light to NEID in an adjacent building. NEID sits in a box within a box within a box. First, there's an outer room cooled slightly below room temperature. In that room sits a "meat locker" operating at the same temperature. Inside the meat locker is a vacuum chamber suspended from cables on a cushion of air. And in that vacuum chamber, the NEID optical bench uses liquid nitrogen-cooled optical detectors that remain temperature-stable within a millionth of a Kelvin.

It's an extreme setup for an extreme instrument, located on an observatory mountaintop in the middle of the desert.

"The mountain goes from negative 5 to 40 degrees Celsius in a year—none of that can get through to the bench," Rajagopal said.

NEID measurements must be repeatable over long periods of time, enough for exoplanets to complete full orbits around their host stars. During that time, operators will inevitably have to take the telescope offline for routine maintenance activities such as cleaning and polishing the mirror. To stay calibrated, the instrument uses a laser frequency comb, which creates a known, artificial spectrum against which to compare results.

If NEID does get to 10 centimeters per second, scientists will face a new challenge: "stellar jitter." At such small scales, star surfaces are not uniform. They balloon, shift, and belch out flares, all of which can throw off radial velocity measurements. Rajagopal said the scientific community is already figuring out ways to filter out these anomalies. For instance, certain star spectral lines represent certain chemical compositions, and stellar jitter acts on those lines in different ways.

"There are certain lines indicative of the photosphere doing something, as opposed to the entire star doing something," said Rajagopal.