A low-eccentricity migration pathway for a 13-h-period Earth analogue in a four-planet system
Authors: Serrano Luisa Maria 
Published: September 2022

&lt;p&gt;It is commonly accepted that exoplanets with orbital periods shorter than one day, also known as ultra-short-period (USP) planets, formed further out within their natal protoplanetary disks before migrating to their current-day orbits via dynamical interactions. One of the most accepted theories suggests a violent scenario involving high-eccentricity migration followed by tidal circularization. Here we present the discovery of a four-planet system orbiting the bright (V=10.5) K6 dwarf star TOI-500. The innermost planet is a transiting, Earth-sized USP planet with an orbital period of nearly 13hours, a mass of 1.42&amp;#177;0.18Earth Masses, a radius of &lt;span class=&quot;mathjax-tex&quot;&gt;&lt;span id=&quot;MathJax-Element-1-Frame&quot; class=&quot;MathJax&quot; tabindex=&quot;0&quot; role=&quot;presentation&quot; data-mathml=&quot;&lt;math xmlns=&quot;&gt;&lt;span id=&quot;MathJax-Span-1&quot; class=&quot;math&quot;&gt;&lt;span id=&quot;MathJax-Span-2&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-3&quot; class=&quot;mn&quot;&gt;1.16&lt;/span&gt;&lt;span id=&quot;MathJax-Span-4&quot; class=&quot;msubsup&quot;&gt;&lt;span id=&quot;MathJax-Span-5&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-6&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-7&quot; class=&quot;mn&quot;&gt;6&amp;#177;0.061 &lt;/span&gt;&lt;/span&gt;&lt;/span&gt;Earth Radii&lt;/span&gt;&lt;span id=&quot;MathJax-Span-17&quot; class=&quot;msubsup&quot;&gt;&lt;span id=&quot;MathJax-Span-19&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-20&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-21&quot; class=&quot;mo&quot;&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt; and a mean density of &lt;span class=&quot;mathjax-tex&quot;&gt;&lt;span id=&quot;MathJax-Element-2-Frame&quot; class=&quot;MathJax&quot; tabindex=&quot;0&quot; role=&quot;presentation&quot; data-mathml=&quot;&lt;math xmlns=&quot;&gt;&lt;span id=&quot;MathJax-Span-22&quot; class=&quot;math&quot;&gt;&lt;span id=&quot;MathJax-Span-23&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-24&quot; class=&quot;mn&quot;&gt;4.8&lt;/span&gt;&lt;span id=&quot;MathJax-Span-25&quot; class=&quot;msubsup&quot;&gt;&lt;span id=&quot;MathJax-Span-26&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-27&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-28&quot; class=&quot;mn&quot;&gt;9&amp;#177;1.03&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt; &lt;/sup&gt;&lt;/span&gt;&lt;sub&gt;&lt;span id=&quot;MathJax-Span-37&quot; class=&quot;mspace&quot;&gt;&lt;/span&gt;&lt;/sub&gt;&lt;span id=&quot;MathJax-Span-38&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-39&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-40&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-41&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-42&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-43&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-44&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-45&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-46&quot; class=&quot;mi&quot;&gt;g&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;span id=&quot;MathJax-Span-47&quot; class=&quot;mspace&quot;&gt;&lt;/span&gt;&lt;span id=&quot;MathJax-Span-48&quot; class=&quot;msubsup&quot;&gt;&lt;span id=&quot;MathJax-Span-49&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-50&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-51&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-52&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-53&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-54&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-55&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-56&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-57&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-58&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-59&quot; class=&quot;mi&quot;&gt;c&lt;/span&gt;&lt;span id=&quot;MathJax-Span-60&quot; class=&quot;mi&quot;&gt;m&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;&lt;span id=&quot;MathJax-Span-61&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-62&quot; class=&quot;mrow&quot;&gt;-&lt;span id=&quot;MathJax-Span-64&quot; class=&quot;mn&quot;&gt;3&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/sup&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;. Via Doppler spectroscopy, we discovered that the system hosts 3 outer planets on nearly circular orbits with periods of 6.6, 26.2 and 61.3 days and minimum masses of 5.03&amp;#177;0.41 Earth Masses, 33.12&amp;#177;0.88 Earth Masses and &lt;span class=&quot;mathjax-tex&quot;&gt;&lt;span id=&quot;MathJax-Element-3-Frame&quot; class=&quot;MathJax&quot; tabindex=&quot;0&quot; role=&quot;presentation&quot; data-mathml=&quot;&lt;math xmlns=&quot;&gt;&lt;span id=&quot;MathJax-Span-65&quot; class=&quot;math&quot;&gt;&lt;span id=&quot;MathJax-Span-66&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-67&quot; class=&quot;mn&quot;&gt;15.0&lt;/span&gt;&lt;span id=&quot;MathJax-Span-68&quot; class=&quot;msubsup&quot;&gt;&lt;span id=&quot;MathJax-Span-69&quot; class=&quot;texatom&quot;&gt;&lt;span id=&quot;MathJax-Span-70&quot; class=&quot;mrow&quot;&gt;&lt;span id=&quot;MathJax-Span-71&quot; class=&quot;mn&quot;&gt;5&amp;#177;1.12 Earth Masses&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt; respectively. The presence of both a USP planet and a low-mass object on a 6.6-day orbit indicates that the architecture of this system can be explained via a scenario in which the planets started on low-eccentricity orbits then moved inwards through a quasi-static secular migration. Our numerical simulations show that this migration channel can bring TOI-500 b to its current location in 2Gyr, starting from an initial orbit of 0.02au. TOI-500 is the first four-planet system known to host a USP Earth analogue whose current architecture can be explained via a non-violent migration scenario.&lt;/p&gt;
&lt;p&gt;Published on Nature Astronomy (https://www.nature.com/articles/s41550-022-01641-y?fbclid=IwAR2fylY1YA8W04j9Y18_-qdx8jpAEWXweTOdJS3MWS2HMRwWpaFDxr9NnQ4)&lt;/p&gt;