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Inside six years of space telescope data, 8,134 faint red stars produced just five trusted sub-Neptunes. <\/p>\n
Erik Gillis is a PhD student in physics and astronomy at McMaster University<\/a>. By analyzing repeated dips in starlight, his team linked the absence of sub-Neptunes to the Milky Way\u2019s most common type of star.<\/p>\n Many super-Earths were still present, suggesting planet formation was still active.<\/p>\n That split points toward a different recipe for planets around the smallest stars, not a simple shortage of worlds.<\/p>\n Watching for dips in starlight<\/p>\n NASA\u2019s Transiting Exoplanet Survey Satellite (TESS<\/a>), a space telescope that tracks changes in star brightness, supplied the raw view.<\/p>\n Each dip in starlight can mark a transit \u2013 a planet crossing in front of its star \u2013 which briefly blocks light.<\/p>\n The team checked how many test signals its software could recover, so missed planets did not masquerade as absence.<\/p>\n After several rounds of filtering, 77 vetted planet candidates remained around 65 stars.<\/p>\n Stars that make up most of the galaxy<\/p>\n Astronomers call the targets mid-to-late M dwarfs \u2013 small, cool stars only eight to 40 percent as large as the Sun. <\/p>\n These stars make up most of the Milky Way, so their planets shape the galaxy\u2019s real average.<\/p>\n Within 30 days of orbit, the survey found a little more than one planet larger than Earth around each star on average. That result shows these small red stars hold a large share of the galaxy\u2019s nearby planets.<\/p>\n Sun-like star surveys<\/a> had drawn a split between super-Earths and sub-Neptunes, with fewer planets in between. <\/p>\n Astronomers call that gap the radius valley, a size range where fewer close-in planets appear.<\/p>\n Earlier studies<\/a> of slightly larger red stars still showed a dip between two common planet sizes. Here, that dip disappears, and most planets cluster around a single, Earth-like size.<\/p>\n A watery explanation<\/p>\n Formation models<\/a> had predicted that the valley could fade when small stars make more water-rich worlds.<\/p>\n In that picture, pebble accretion<\/a> \u2013 planet growth from drifting grains and ice \u2013 packs water into young planets early.<\/p>\n Water can increase a planet\u2019s size without requiring a thick gas envelope, allowing some worlds to blur the usual boundary. <\/p>\n This idea could explain the missing sub-Neptunes, but confirming it will require measurements of their masses and atmospheres.<\/p>\n The mechanism remains mysterious <\/p>\n Intense starlight can strip gas from a young planet in a process known as photoevaporation<\/a>.<\/p>\n That mechanism should be strong around active red stars because high-energy radiation heats upper air until gas escapes. <\/p>\n However, Gillis\u2019s team found too few sub-Neptunes for stripping alone to explain the pattern cleanly.<\/p>\n \u201cAround these stars, sub-Neptunes effectively vanish, which means the mechanisms shaping planets here are different,\u201d said Gillis.<\/p>\n Blind spot in the data<\/p>\n Careful filters removed many false positives \u2013 signals that look like planets but are not \u2013 before the final count.<\/p>\n Software rejected 427 of 532 initial signals, and later checks narrowed the sample to 77 candidates.<\/p>\n Survey sensitivity dropped for smaller planets and longer orbits, especially beyond 14 days for many targets.<\/p>\n Because of that blind spot, the numbers say less about tiny Earth-size worlds far from their stars.<\/p>\n That caution also applies to future searches for life within the habitable zone<\/a> \u2013 the range of orbits where liquid surface water could exist.<\/p>\n Classic calculations<\/a> mark that zone by tracking when incoming starlight drives water loss or freezing.<\/p>\n For rocky planets close to Earth\u2019s size, the stricter habitable zone holds fewer than about one in three stars with such a world.<\/p>\n \u201cIf we want to understand the origins of planets and the origins of life, we need a complete picture of how planets form and what they\u2019re made of,\u201d said Gillis.<\/p>\n Giant worlds stay rare<\/p>\n Large worlds stayed scarce across the same search, which found no Neptune-size planets among the trusted candidates.<\/p>\n A single Jupiter-size signal turned out to be a brown dwarf \u2013 an object heavier than a planet but lighter than a star.<\/p>\n With no true hot Jupiters<\/a> \u2013 Jupiter-size planets orbiting very close to their stars \u2013 the survey set a ceiling of 0.012 per star within 10 days.<\/p>\n That rarity helps explain why the smallest stars mostly offer compact worlds rather than giant neighbors.<\/p>\n By linking missing sub-Neptunes, plentiful super-Earths, and a vanishing radius valley, the survey redraws the most common planetary neighborhood.<\/p>\n The next step is to measure the planets\u2019 masses and analyze their atmospheres, since size reveals the pattern but not their composition.<\/p>\n The study is published in The Astronomical Journal<\/a>.<\/p>\n Image Credit: NASA<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"The galaxy\u2019s most common stars almost never host sub-Neptunes, planets smaller than Neptune but larger than Earth, according…\n","protected":false},"author":2,"featured_media":413243,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[111,139,69,147,392],"class_list":["post-413242","post","type-post","status-publish","format-standard","has-post-thumbnail","category-space","tag-new-zealand","tag-newzealand","tag-nz","tag-science","tag-space"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/413242","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=413242"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/413242\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/413243"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=413242"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=413242"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=413242"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}