Observation Edit

Artist's conception of a Jupiter -size rogue planet. Astrophysicist Takahiro Sumi of Osaka University in Japan and colleagues, who form the Microlensing Observations in Astrophysics and the Optical Gravitational Lensing Experiment collaborations, published their study of microlensing in 2011. They observed 50 million stars in the Milky Way using the 1.8-meter MOA-II telescope at New Zealand's Mount John Observatory and the 1.3-meter University of Warsaw telescope at Chile's Las Campanas Observatory. They found 474 incidents of microlensing, ten of which were brief enough to be planets of around Jupiter's size with no associated star in the immediate vicinity. The researchers estimated from their observations that there are nearly two Jupiter-mass rogue planets for every star in the Milky Way.[9][10][11] Other estimates suggest a much larger number, up to 100,000 times more rogue planets than stars in the Milky Way.[12] A 2017 study by Przemek Mróz of Warsaw University Observatory and colleagues, with six times larger statistics than the 2011 study, indicates an upper limit on Jupiter-mass free-floating or wide-orbit planets of 0.25 planets per main-sequence star in the Milky Way.[13] Nearby rogue planet candidates include WISE 0855−0714 at a distance of 7000727000000000000♠7.27±0.13 light-years.[14]

Retention of heat in interstellar space Edit

Interstellar planets generate little heat and are not heated by a star.[15] In 1998, David J. Stevenson theorized that some planet-sized objects adrift in interstellar space might sustain a thick atmosphere that would not freeze out. He proposed that these atmospheres would be preserved by the pressure-induced far-infrared radiation opacity of a thick hydrogen-containing atmosphere.[16] During planetary-system formation, several small protoplanetary bodies may be ejected from the system.[17] An ejected body would receive less of the stellar-generated ultraviolet light that can strip away the lighter elements of its atmosphere. Even an Earth-sized body would have enough gravity to prevent the escape of the hydrogen and helium in its atmosphere.[16] In an Earth-sized object that has a kilobar atmospheric pressure of hydrogen and a convective gas adiabat, the geothermal energy from residual core radioisotope decay could maintain a surface temperature above the melting point of water,[16] allowing liquid-water oceans to exist. These planets are likely to remain geologically active for long periods. If they have geodynamo-created protective magnetospheres and sea floor volcanism, hydrothermal vents could provide energy for life.[16] Thus, humans could live on such a star-less planet, although food sources would be limited. These bodies would be difficult to detect because of their weak thermal microwave radiation emissions, although reflected solar radiation and far-infrared thermal emissions may be detectable from an object that is less than 1000 astronomical units from Earth.[18] Around five percent of Earth-sized ejected planets with Moon-sized natural satellites would retain their satellites after ejection. A large satellite would be a source of significant geological tidal force heating.[19]

Known or possible rogue planets Edit

See also Edit

Intergalactic star – A star not gravitationally bound to any galaxy

Rogue comet

Rogue extragalactic planets – Rogue planets that are outside the Milky Way galaxy

References Edit