Tau Ceti e

Tau Ceti is one of the closest stars like the Sun, about 11.9 light-years away in the constellation Cetus. For more than a decade, it was thought to have a planet that might be habitable: Tau Ceti e, a world at least four times Earth’s mass. In March 2026 it starred, as “Adrian”, in the film Project Hail Mary. Three weeks later, NASA’s Exoplanet Archive reclassified it as a false positive. It is probably not there.

A planet found in the noise

Tau Ceti e was never seen. It was inferred from tiny back-and-forth shifts in the star’s light, the radial-velocity method, which detects the wobble a planet’s pull gives its star. In 2012 Tuomi and colleagues combed through years of measurements and reported five candidate signals. One, with a period of 168 days, would put a planet inside the zone where liquid water could exist, though they called that “merely speculative”.

In 2017 Feng and colleagues reanalysed the data. They dropped three of the candidates, kept two, including e, and added two more. In their version Tau Ceti e circled every 162.87 days at 0.538 AU, with at least 3.93 times Earth’s mass, placing it outside the conservative habitable zone and close to the inner edge of the optimistic one. The wobble it caused was only 0.55 metres per second, slower than a person walking.

The test it failed

The ESPRESSO spectrograph on ESO’s Very Large Telescope can measure a star’s motion to better than 10 centimetres per second. In 2025 Figueira and colleagues used it on Tau Ceti and found nothing. A planet of 3.93 Earth masses on a 162-day orbit, they wrote, “should have been detected”. On 9 April 2026 the archive changed its status to “False Positive Planet” and removed it from its planet tables. NASA’s own page on Project Hail Mary says studies in 2024 and 2025 found the Tau Ceti signals were likely quirks of data analysis or activity on the star itself.

There was another problem. In 2023 Korolik and colleagues found that Tau Ceti is seen almost exactly pole-on, its axis tilted only 7 degrees, give or take 7, from our line of sight. If the planets orbited in line with the star’s equator, their true masses would be far larger than the minimum values, and the four-planet system as proposed might not stay stable.

What is really there

Tau Ceti itself is real and well studied: a yellow-orange star about 0.80 times the Sun’s width, at 5 382 K (5 110 °C). Around it lies a broad belt of dust and comets stretching out to about 55 AU, with at least ten times the dust of our own Kuiper Belt. Whatever planets Tau Ceti has, they share their system with far more debris than ours does. Its remaining candidates, f, g and h, are still listed by the archive.