{"id":13876,"date":"2025-04-08T22:00:00","date_gmt":"2025-04-08T22:00:00","guid":{"rendered":"https:\/\/modernsciences.org\/staging\/4414\/?p=13876"},"modified":"2025-03-28T07:40:53","modified_gmt":"2025-03-28T07:40:53","slug":"exoplanet-discovery-barnards-star-red-dwarf-habitable-zone-astronomy-research-april-2025","status":"publish","type":"post","link":"https:\/\/modernsciences.org\/staging\/4414\/exoplanet-discovery-barnards-star-red-dwarf-habitable-zone-astronomy-research-april-2025\/","title":{"rendered":"Four small planets discovered around one of the closest stars to Earth \u2013 an expert explains what we\u00a0know"},"content":{"rendered":"\n\n
\n\n Coel Hellier<\/a>, Keele University<\/a><\/em><\/span>\n\n

Barnard\u2019s Star is a small, dim star, of the type that astronomers call red dwarfs<\/a>. Consequently, even though it is one of the closest stars to Earth, such that its light takes only six years to get here, it is too faint to be seen with the naked eye. Now, four small planets have been found<\/a> orbiting the star. Teams in America and Europe achieved this challenging detection by exploiting precision instruments on the world\u2019s largest telescopes. <\/p>\n\n

Diminutive Barnard\u2019s Star is closer in size to Jupiter than to the Sun. Only the three stars that make up the Alpha Centauri system lie closer to us. <\/p>\n\n

The planets newly discovered around Barnard\u2019s Star are much too faint to be seen directly, so how were they found? The answer lies in the effect of their gravity on the star. The mutual gravitational attraction keeps the planets in their orbits, but also tugs on the star, moving it in a rhythmic dance that can be detected by sensitive spectrograph<\/a> instruments. Spectrographs split up the star\u2019s light into its component wavelengths. They can be used to measure the<\/a> star\u2019s motion. <\/p>\n\n

A significant challenge for detection, however, is the star\u2019s own behaviour. Stars are fluid, with the nuclear furnace at their core driving churning motions that generate a magnetic field (just as the churning of Earth\u2019s molten core produces Earth\u2019s magnetic field). The surfaces of red dwarf stars are rife with magnetic storms. This activity<\/a> can mimic the signature of a planet when there isn\u2019t one there.<\/p>\n\n\n\n

The task of finding planets by this method starts with building highly sensitive spectrograph instruments. They are mounted on telescopes large enough to capture sufficient light from the star. The light is then sent to the spectrograph which records the data. The astronomers then observe a star over months or years. After carefully calibrating the resulting data, and accounting for stellar magnetic activity, one can then scrutinise the data for the tiny signals that reveal orbiting planets.<\/p>\n\n

In 2024, a team led by Jonay Gonz\u00e1lez Hern\u00e1ndez from the Canary Islands Astrophysics Institute reported on<\/a> four years of monitoring of Barnard\u2019s Star with the Espresso<\/a> spectrograph on the European Southern Observatory\u2019s Very Large Telescope in Chile. They found one definite planet and reported tentative signals that indicated three more planets. <\/p>\n\n

Now, a team led by Ritvik Basant from the University of Chicago in a paper<\/a> just published in Astrophysical Journal Letters, have added in three years of monitoring with the Maroon-X<\/a> instrument on the Gemini North telescope. Analysing their data confirmed the existence of three of the four planets, while combining both the datasets showed that all four planets are real.<\/p>\n\n

Often in science, when detections push the limits of current capabilities, one needs to ponder the reliability of the findings. Are there spurious instrumental effects that the teams haven\u2019t accounted for? Hence it is reassuring when independent teams, using different telescopes, instruments and computer codes, arrive at the same conclusions. <\/p>\n\n

\n \"Gemini\n
\n The Gemini North telescope is located on Maunakea in Hawaii.<\/span>\n MarkoBeg \/ Shutterstock<\/a><\/span>\n <\/figcaption>\n <\/figure>\n\n

The planets form a tightly packed, close-in system, having short orbital periods of between two and seven Earth days (for comparison, our Sun\u2019s closest planet, Mercury, orbits in 88 days). It is likely they all have masses less than Earth\u2019s. They\u2019re probably rocky planets, with bare-rock surfaces blasted by their star\u2019s radiation. They\u2019ll be too hot to hold liquid water, and any atmosphere is likely to have been stripped away. <\/p>\n\n

The teams looked for longer-period planets, further out in the star\u2019s habitable zone, but didn\u2019t find any. We don\u2019t know much else about the new planets, such as their estimated sizes. The best way of figuring that out would be to watch for transits, when planets pass in front of their star, and then measure how much starlight they block. But the Barnard\u2019s Star planets are not orientated in such a way that we see them \u201cedge on\u201d from our perspective. This means that the planets don\u2019t transit, making them harder to study.<\/p>\n\n

Nevertheless, the Barnard\u2019s Star planets tell us about planetary formation. They\u2019ll have formed in a protoplanetary disk<\/a> of material that swirled around the star when it was young. Particles of dust will have stuck together, and gradually built up into rocks that aggregated into planets. Red dwarfs are the most common type of star, and most of them seem to have planets. Whenever we have sufficient observations of such stars we find planets, so there are likely to be far more planets in our galaxy than there are stars.<\/p>\n\n

Most of the planets that have been discovered are close to their star, well inside the habitable zone (where liquid water could survive on the planet\u2019s surface), but that\u2019s largely because their proximity makes them much easier to find. Being closer in means that their gravitational tug is bigger, and it means that they have shorter orbital periods (so we don\u2019t have to monitor the star for as long). It also increases their likelihood of transiting, and thus of being found in transit surveys. <\/p>\n\n

The European Space Agency\u2019s Plato mission<\/a>, to be launched in 2026, is designed to find planets further from their stars. This should produce many more planets in their habitable zones, and should begin to tell us whether our own solar system, which has no close-in planets, is unusual.\"The<\/p>\n\n

Coel Hellier<\/a>, Professor of Astrophysics, Keele University<\/a><\/em><\/span><\/p>\n\n

This article is republished from The Conversation<\/a> under a Creative Commons license. Read the original article<\/a>.<\/p>\n<\/div>\n\n\n\n\n

<\/p>\n\n\n\n

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