The stars twinkle with a stubborn stubbornness that makes planets feel almost invisible, until a spectrograph like NEID learns to hear their tiny wobbles. Over three years, a dedicated team has been listening to 41 nearby stars with extraordinary care, chasing the faint tug of Earth-like worlds in the quietest corners of our solar neighborhood. The project—NEID Earth Twin Survey, or NETS for short—has mapped a trajectory from careful planning to surprisingly sharp detections, all while wrestling with instrument drift, telluric noise, and the stubborn rhythms of the stars themselves. And the headline isn’t just about new planets; it’s about how close we are to characterizing Earth-like worlds around other suns with a precision that used to feel out of reach.
The paper describing NETS after three years is a milestone in a field that prizes patience as much as ingenuity. Authored with Arvind F. Gupta as the corresponding author, the study is a collaboration among institutions that span NOIRLab at the National Science Foundation, Penn State, Caltech’s Jet Propulsion Laboratory, UCI, Amherst, and more. In the words of Gupta and colleagues, this is a survey designed to push sub-m/s radial-velocity precision into the realm where Earth-like planets exert their gently discouraging influence on a sunlike star. The project sits at the intersection of engineering discipline, long-term planning, and the stubborn elegance of statistics—an astronomy version of long-distance running, where the finish line keeps wobbling but the pace matters.
What makes NETS special isn’t just the instrument—NEID is a stabilized, fiber-fed spectrograph that covers a broad swath of optical light with an internal precision target around 27 cm s−1. It’s also the strategy: a carefully designed cadence, seasonal scheduling, and a data-analysis pipeline that treats every run as a chapter in a single narrative. After three years, NETS has delivered a full set of RV measurements and activity indicators for its 41 targets, complete with the quirks of instrument resets, calibration offsets, and the inevitable surprises that come with real, on-sky data. This isn’t merely a catalog of planets; it’s a proof of concept for how to run a precision survey that could underpin a future era of Earth-like planet demographics and atmospheric studies.
A patient hunt for Earth twins
To understand why NETS matters, imagine trying to hear a whisper in a crowded stadium. The whisper is the gravitational tug of a small planet; the stadium is the star’s own jitter—its rotation, magnetic activity, and the subtle variability of its surface. NETS addresses this with a two-pronged approach: push the spectrograph’s stability to the limit and design an observing cadence that teases apart planetary signals from stellar noise. The result is a dataset that, on its own, can reveal planets with semi-amplitudes down to a few meters per second and, in some cases, down to well under a meter per second. That’s the scale at which Earth-like planets begin to whisper their presence in the radial-velocity record.
At the heart of NETS is a deliberate observational cadence. Each star is sampled with a nearly uniform single-measurement precision, but the cadence is highly structured: a mid-season high-cadence block (P1) to catch rotationally modulated activity; a longer-baseline, lower-cadence component (P2) to improve phase coverage for longer-period signals; and a season-bracketing, short-term set (P0) to keep the schedule robust against the inevitable gaps caused by weather or maintenance. The point is not to maximize the number of detections per night, but to construct a time series that can separate the star’s own heartbeat from the faint pulse of a planet. The strategy—and the discipline behind it—are what allow NETS to approach the sensitivity of decades of RV monitoring in just three years.
In these pages, the authors trace how the survey weathered interruptions—the Contreras wildfire-driven shutdown in 2022, a temporary etalon calibration outage, and a telescope-mirror failure later that year. They show how, even after those disruptions, the core design held, and the timeframe still yielded meaningful conclusions about the survey’s capabilities. The hidden story isn’t only in the planets NETS recovered; it’s in the experiment’s resilience, in the way the team recalibrated the instrument’s zero points, and in how they distinguished genuine planetary signals from instrument quirks. That discipline matters because the future of Earth-like exoplanet science will depend on reliability as much as resolution.
How NEID squeezes cm s−1 precision from starlight
NEID is a triumph of engineering and calibration, designed to stabilize the wavelength scale and the shape of spectral lines to an astonishing degree. The instrument’s design aims at internal precision better than 27 cm s−1, and on-sky tests have demonstrated precision below 50 cm s−1. It’s not just the hardware; it’s the entire pipeline: how the light is fed through fibers, how the spectrograph is temperature-controlled, and how the calibration system anchors every velocity measurement to a robust reference. The NETS paper makes clear that the real magic happens when hardware meets strategy.
Over the three-year baseline, the NETS team documented two notable episodes that illustrate the fragility and the fixability of high-precision RV work. First, two zero-point shifts in the RV scale appeared in Run 0.5 and Run 1, then Run 2, linked to changes in the instrument environment and to the spectrograph’s wavelength-calibration chains. The first era shift (Run 0.5 to Run 1) was modest, about 0.7 m s−1 on average, but not negligible for planet hunting. The second shift (Run 1 to Run 2) was more pronounced and traced, in part, to a new ThAr master wavelength solution and the instrument’s response to a thermal cycle after the wildfire shutdown. What this reveals is not a flaw, but a map: it shows how careful cross-era corrections and chromatic analyses are essential when you push toward sub-meter-per-second territory.
One especially instructive finding concerns chromatic offsets. The team found that, for the Run 1 to Run 2 transition, the offset varied strongly with wavelength in the blue part of the spectrum, anchored to the ThAr calibration orders, while the redder orders, anchored to a laser frequency comb, showed essentially zero offset. That nuance matters because many stars are cooler or warmer, and a chromatic offset can masquerade as a planetary signal if not properly accounted for. NETS’ approach—examining the offset as a function of wavelength and separating ThAr-anchored orders from LFC-anchored orders—provides a blueprint for how to disentangle instrumental drift from real astrophysical signals. It’s the kind of careful accounting that future Earth-twin surveys will need to scale up.
Beyond instrument quirks, NETS leverages the star’s own activity indicators. The NEID data stream includes contemporaneous measurements of Ca II H&K, Hα, and other activity proxies, which lets the team separate rotational modulation and magnetic cycles from genuine Doppler shifts due to planets. As the authors note, these activity indicators do not carry the same wavelength-dependent shifts as the RV tracks, so they serve as a compass for interpreting the RV time series. In practice, this means a planet’s signal can survive a forest of stellar noise if you hold the right indicators in view.
What three years of NETS reveal about planets and stars
The most striking takeaway is the survey’s demonstrated sensitivity: with only three years of dedicated NEID observations, NETS is approaching the sensitivity of decades of RV monitoring for its target stars, at least for signals with periods shorter than the observing baseline. In other words, the team is proving that a modern, well-structured campaign can catch the small, slow gravitational tugs of rocky planets in or near the habitable zones of nearby stars. The data show that several known short-period planets—some with semi-amplitudes down to a couple meters per second or less—are independently recoverable using NETS data alone. That’s a meaningful milestone: it validates the instrument, the cadence strategy, and the analysis pipeline in a way that stands without leaning on historical measurements.
The authors separate the stars into two camps: those with long-period companions (planetary or stellar) and those without. For the long-period systems, the current baseline simply isn’t long enough to claim independent detections of the outer planets. But NETS does more than test sensitivity to known signals; it also reveals potential new signals in several systems, signals that warrant follow-up with longer baselines and, when possible, joint analyses that blend archival RVs with NETS data. The thrill here isn’t a flood of new worlds, but the emergence of credible planet candidates and the demonstration that mature, stable instrumentation can distinguish small planetary signals from the noise of stars.
Some of the most compelling stories come from specific stars. For instance, in the well-known HD 190360 system, the survey recovers the inner, shorter-period planet consistent with prior work and hints at a second signal that could be a new planet candidate—a finding aligned with recent joint RV+astrometric studies. In other systems with long-standing planet schedules, NETS can reframe what we know by providing precise, era-tagged RVs that help separate long-period planetary motion from long-term activity cycles. The upshot is a more reliable census of planets around these bright, quiet stars, and a path toward mass measurements that can feed into atmospheric modeling for future missions.
Why does this matter for the next generation of exoplanet exploration? Because a space-based mission designed to characterize Earth-like atmospheres—such as the Habitable Worlds Observatory (HWO) envisioned in recent decadal planning—relies on precise planetary masses to interpret spectral fingerprints. If we don’t know the mass to a few percent, the inferred atmospheric composition, pressure, and potential biosignatures risk being misread. NETS aims to provide the essential mass priors and orbital architectures that will make HWO-era observations far more informative. The authors point to a synergy: ground-based, centimeter-level RV precision can unlock the atmospheric secrets of Earth-like worlds from space by constraining the planets’ gravitational influence with high fidelity.
Beyond planets, the NETS story also teaches a broader scientific lesson: even a state-of-the-art instrument can drift, and the drama of discovery requires a robust framework for diagnosing and correcting those drifts. The team’s careful accounting of zero-point offsets, the chromatic nature of some systematics, and the integration of activity indicators into the analysis all illustrate a mature scientific workflow. That workflow is exactly what future EPRV surveys will need as they push toward even longer baselines, fainter stars, and smaller planets. In a sense, NETS is rehearsing the choreography that will enable the next leap—when we’ll routinely weigh a truly Earth-like world and glimpse its atmosphere with a clarity that today still feels aspirational.
So what did NETS accomplish in three years? It delivered a precise, multi-faceted data trove for 41 nearby stars, showcased the stability and calibration strategies required for sub-meter-per-second precision, demonstrated the ability to independently recover most known short-period planets, and laid out a clear roadmap for handling long-period signals and instrument changes. It also surfaced candidate signals that deserve further attention, a reminder that even in a field with decades of data, there remains the potential for new worlds to whisper into the RV record as our listening grows more attentive. The study’s closing message is both practical and hopeful: with continued monitoring and methodological care, NETS can build the mass measurements and dynamical constraints that turn “Earth-like” from a dream into a testable scientific claim.
As the paper concludes, the NETS target list includes several high-priority stars for future space missions. The road ahead isn’t merely about finding new planets; it’s about ensuring we know enough about the ones we already sense to interpret their atmospheres with confidence. The three-year milestone is less a finish line than a milestone marker in a longer journey toward a census of nearby Earth analogs, and toward understanding how stellar habitability plays out in practice around real stars. In that sense, NETS isn’t just about detecting worlds; it’s about shaping the questions we’ll be asking when we finally peer at their skies with their own, alien weather in view.
Institutional backbone and leadership: The NETS effort is led by Arvind F. Gupta of NOIRLab, with major contributions from Penn State’s Center for Exoplanets and Habitable Worlds and related facilities, including collaborations across The University of California, Irvine, Amherst College, NASA Goddard Space Flight Center, and JPL. The lead author is Gupta, and the paper acknowledges a broad consortium of researchers who helped design, execute, and interpret the three-year dataset. This is a reminder that frontier science today rests on the partnership of institutions—university laboratories, national observatories, and space-era instrumentation—that together push the envelope of what a single telescope can reveal.
