Their measurements combine space and ground-based telescopes and appear in the journal Science.<\/p>\n
A planetary system that runs \u201cinside out\u201d<\/p>\n
The star LHS 1903 is a small, faint red dwarf<\/a> in the thick disk of the Milky Way, cooler and dimmer than our Sun. Around it, astronomers have found four planets that circle the star in just a few days to about one month.<\/p>\n Closest in, LHS 1903 b is a dense rocky world. Next come two larger planets, LHS 1903 c and LHS 1903 d, which have puffy gas-rich envelopes more like mini Neptunes. The surprise is LHS 1903 e, the most distant planet, which turns out to be small and rocky again instead of another gas-dominated world.<\/p>\n \u201cThis strange disorder makes it a unique inside out system,\u201d Dr. Wilson said, noting that rocky planets usually huddle closer to their star. <\/p>\n In everyday terms, it is like finding a compact studio apartment on the outskirts of town, with two large suburban houses tucked between it and the city center. The pattern \u201crocky gas gas rocky\u201d simply does not match what most models predict.<\/p>\n How planets are supposed to form<\/p>\n In our own solar system, Mercury through Mars are rocky, while Jupiter through Neptune are gaseous giants or ice-rich worlds. That basic trend also shows up in many other planetary systems, where inner planets are heated so strongly that much of their gas is stripped away, leaving solid cores behind. <\/p>\n Farther out, where starlight is weaker and cooler, planets can hold onto thick atmospheres of hydrogen and helium.<\/p>\n Over the past decade, surveys with space telescopes have revealed a \u201cradius valley\u201d in the sizes of small exoplanets<\/a>, a gap between compact super Earths<\/a> and slightly larger sub Neptunes that hints at how atmospheres are lost or never gained in the first place. <\/p>\n The LHS 1903 planets sit right across that valley inside a single system, which makes them a kind of natural laboratory for studying how rocky and gas-rich planets diverge.<\/p>\n On paper, the outer planet should have followed the same basic script as its neighbors and ended up with at least a modest gas envelope. Instead, its measured density suggests bare rock. So something about when or where it formed must have been different.<\/p>\n Cheops and TESS track a late bloomer<\/p>\n The planets around LHS 1903 were first spotted through tiny dips in the star\u2019s brightness using NASA\u2019s Transiting Exoplanet Survey Satellite, better known as TESS. <\/p>\n
![\"An](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2026\/04\/lhs-1903-inverted-planetary-system-rocky-planets-1.jpg\" "\\"Astronomers")
The LHS 1903 system features a small rocky planet at its outer edge, a placement that contradicts standard theories of how planets form.<\/p>\n