Physicist Richard Muller says unseen star sends comets toward Earth

Physicist Richard Muller of the University of California, Berkeley said by phone that an undiscovered low-mass red dwarf called Nemesis, orbiting the Sun around a common center of gravity, perturbs long-period comets from the Oort cloud, a theoretical shell of icy bodies surrounding the solar system, in remarks published Nov. 7, 2026 and Nov. 9, 2026.

Phys.org and Universe Today report that the Oort cloud is a theoretical, largely spherical cloud of trillions of icy bodies left over from the solar system’s formation 4.5 billion years ago, extending up to 1.6 light-years from the Sun — a light-year is the distance light travels in a year. The cloud remains heretofore unseen and a mystery despite its inferred existence from comet orbits.:

Muller said Nemesis follows a slightly eccentric oval orbit around the Oort cloud and periodically perturbs billions of comets, with each close approach sparking a comet shower lasting about a million years. He said Nemesis must be at least 5 percent the mass of the Sun to be large enough to perturb the cloud.

Muller said Nemesis avoids detection because it moves with the Sun around their common center of gravity, producing too little proper motion — its apparent shift against background stars — across the line of sight to be detected. He said it likely lies close to the ecliptic plane, the plane of Earth‘s orbit, as a dim eighth- or ninth-magnitude star, making it impossible to see with the naked eye.:

Muller said he still supports the Nemesis hypothesis, is not optimistic about directly observing Nemesis, and sees no clear evidence against it. His uncertainty about direct observation reflects the difficulty of spotting a distant, dim object amid background stars. He said the next comet shower capable of serious damage to Earth should not arrive for another 12 to 15 million years.:

Astronoo reports that the Nemesis hypothesis originated in 1984 when Richard Muller, Marc Davis, and Piet Hut published in Nature proposing that a companion star in a highly elliptical orbit disturbs Oort cloud comets and increases Earth impacts. The 1984 Nature papers by two independent teams gave rise to the Nemesis or Death Star label and framed the companion as a driver of comet showers.:

Muller said one extinction peak in a 26-million-year marine extinction record occurred 66 million years ago at the K-T boundary, which wiped out the dinosaurs. David Raup and Jack Sepkoski collected that record in a 1982 paper in Science, and he said plotting those extinctions reveals a strong 26-million-year period.:

Muller said Nemesis is responsible for 250 million years of clearly defined periodic Earth impacts and is neither Planet X nor random stellar interlopers. He proposed that a companion star approaches the Oort cloud every 26 million years and triggers a comet strike on Earth.:

Phys.org and Universe Today report that the consensus view holds that the K-T extinction 66 million years ago at the Yucatan Peninsula was most likely caused by a large asteroid, though Muller said the asteroid-versus-comet evidence is very weak. He said Walter Alvarez told him scientists could not tell whether the K-T impactor was an asteroid or a comet, and Alvarez initially identified the impactor as an asteroid in his boundary paper.:

Astronoo also describes it as a zone from 2,000 to 100,000 AU — an AU is the distance from Earth to the Sun — holding billions of dark icy bodies inferred from a few long-period comets arriving from all directions. This defines the cloud’s scale and explains why its existence rests on a few observed comets.

Sean Raymond, director of France’s Bordeaux Astrophysical Laboratory, said Oort cloud material came from planetesimals in the Sun’s planet-forming disk, planetesimals around other stars in the Sun’s birth cluster, and captured interstellar objects.

Astronoo reports that alternative explanations for Oort cloud perturbations include close passages of other stars and the Milky Way’s tidal force, known as the Shiva hypothesis, which do not require a companion star. Galactic tides and stellar passages provide natural mechanisms for disturbing the Oort cloud without invoking Nemesis.

Chameleon Magazine reports that the Sun probably formed with many other stars in a stellar nursery around 4.6 billion years ago, and its siblings scattered across the Milky Way. The Sun moves around the Milky Way at roughly 230 km/s, and stellar encounters are real, but Chameleon Magazine said a permanent second Sun orbiting it is unlikely.

Using Gaia data, astronomers can calculate some future close approaches of stars to the Solar System, Chameleon Magazine reports. Stellar-motion reconstructions make the flyby alternative testable and observable in advance.

Astronoo reports that a 2017 paper by Sarah Sadavoy and Steven Stahler argued the Sun was probably part of a binary system at formation, but any companion separated over four billion years ago and cannot explain extinction cycles. Most massive stars are seen in multiple systems, a share of 70 percent, implying the Sun’s alone status is probably not primordial.:

Astronoo reports that the Wide-field Infrared Survey Explorer, or WISE, has not detected Nemesis, though it can detect brown dwarfs as cool as 150 kelvin out to 10 light-years from the Sun. WISE data rules out warm, massive dwarfs or red dwarfs inside roughly 1.5 light-years of the Sun. The Infrared Astronomical Satellite failed to discover Nemesis in the 1980s, and the 2MASS survey from 1997 to 2001 failed to detect an additional star or brown dwarf in the Solar System.:

Phys.org and Universe Today report that the Rubin Observatory, coming online, offers the best near-term chance to characterize the Oort cloud by detecting more long-period Oort cloud comets. It is presented as the most immediate observational prospect for expanding that catalog.: