Smaller than the Moon: Astronomers find traces of the smallest exoplanet

An international team of researchers has announced the discovery of traces of the smallest known exoplanet to date. It is part of an exotic triple system that includes a pulsar.

An exoplanet orbiting a pulsar in an artist’s impression. Source: NASA/JPL-Caltech

The discovery was made while studying the pulsar PSR J0337+1715, located 4,200 light-years from Earth in the constellation Taurus. It is a neutron star with a strong magnetic field, rotating at 366 times per second. PSR J0337+1715 is interesting because it is part of a triple system. The pulsar is in a very close orbit with a white dwarf whose mass is 0.2 solar masses. They make one orbit around each other in just 1.6 days.

The third component of this system is also a white dwarf. It has a mass of 0.4 solar masses and orbits around the central pair, making one orbit in 327 days. The fact that all of this trio are located within a perimeter comparable to the size of the Earth’s orbit makes it an ideal natural laboratory for studying gravity and testing various positions of the theory of relativity.

While studying the pulsar, astronomers noticed a shift in the time of arrival of its signals. They indicate the presence of some object causing perturbations of the pulsation period. After checking all the data, astronomers concluded that the shifts are caused by an object whose mass is only half that of the Moon. It orbits the pulsar with a period of 3,310 days.

Illustration of PSR J0337+1715 system. Source: CC-BY-SA Guillaume Voisin & Fabrice Mottez, 2024

According to the researchers, since the object’s orbit is relatively stable, it may be the last surviving member of the small-body population. They formed after the progenitor of the pulsar turned into a red supergiant and swallowed one of the other two stars. This led to them sharing a common shell. The swallowed star was braked by the envelope gas, transferring its orbital energy to it. As a result, it was ejected, and it created a disc around the system, where many smaller objects condensed out of it. Since all the others were in less stable orbits, they were subsequently either ejected from the system or crashed into one of the stars.

Scientists say they will need additional observations to clarify the nature of the object. If confirmed, it would become the smallest known exoplanet to date.

Earlier we reported on how “mountains” on neutron stars could create ripples in space-time.

According to Astrobiology.com

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