An Earth analog or Earth twin planet is defined as any planet which shares most of the characteristics found here on our own planet, including geological processes and lifeforms. Astrobiologists and astronomers study such planets in search of extraterrestrial life forms.
Scientists have recently identified an increasing number of rocky exoplanets – planets like Earth that orbit other stars – with Proxima Centauri b being one of the closest, located only four light-years from its host star and potentially within its habitable zone.
Size
As scientists continue their search for exoplanets like Earth, their search for lifelike planets becomes ever-more focused. But for any planet to meet this criteria and qualify as Earth-like, certain criteria must be fulfilled: it must be rocky and orbit within its host star’s habitable zone – which refers to distances where liquid water can exist on a planet’s surface – for it to qualify as Earth-like.
New research published in Nature adds another condition for planet formation to this list: it must also be tidally locked. Tidally locked planets rotate once every 24 hours so that one side always faces towards their host star – similar to how Earth faces our Moon; this enables tidally locked planets to provide constant sources of energy which sustain life on their surfaces.
Scientists recently made history when they announced they have discovered two tidally locked planets within 16 light-years of each other that are relatively close together (less than 16 light-years apart). Kepler-186f is 95% Earth-sized and likely rocky; its orbit around its star takes 28 days. Meanwhile, outerworld LP 890-9c may be too warm to sustain life, and is thought to likely be locked to its star tidally just like Earth and Moon are. Astronomers believe both planets may also likely be locked tidally like Earth is to its Moon tidally locked to its Sun, just like Earth and Moon are to each other tidally locked like Earth is to its Moon.
People often guess Venus when asked which planet is nearest Earth, but this may not always be accurate. By calculating the average distances between Venus and Mars as well as Mercury from all other planets in our Solar System, Mercury emerges as being closest. This could be because we typically measure distance by subtracting their average distances from the Sun; this does not take into account that planets sometimes spend long stretches apart from each other.
Astronomers recently unveiled Proxima Centauri b, which may be our closest Earth-like planet yet. Only four light years away and with similar orbital dynamics to Earth’s sun, Proxima Centauri b may support life – although its parent star produces large amounts of ultraviolet radiation which could strip its atmosphere and destroy organic molecules that support life on the surface.
Atmosphere
Astronomers at NASA’s Transiting Exoplanet Survey Satellite (TESS) discovered the closest planet similar to earth may possess an atmosphere rich with water vapor. This finding was confirmed using TESS to monitor brightness of thousands of stars; when planets pass in front of stars, their light dims and can be detected by TESS; this information then allows astronomers to confirm and characterize planets; in this instance it was noticed that its atmosphere absorbs near-infrared light from its host star indicating water vapor as well as possibly methane or other gases present indicating its composition.
GJ 1132b’s proximity to its sun suggests it could be tidally locked, with one side always facing toward its star and one remaining perpetually in shadow. Such conditions would likely prove hostile for life as we know it; however, they offer an opportunity for robotic space exploration with future missions like Breakthrough Starshot.
Proxima Centauri b, discovered since 2016, is another potential rocky planet with an atmosphere. This planet orbits our nearest star and sits within its habitable zone – meaning liquid water could potentially exist on its surface – potentially giving life support systems a place to thrive. Proxima Centauri b is approximately four times larger than our own planet and takes 11.2 days to make an orbit around its star.
Earth, Venus, Mars and Jupiter each possess substantial atmospheres made up of hydrogen, carbon dioxide and other gases; none of these planets contains significant quantities of molecular oxygen. Pluto and Titan may have some trace atmospheres when in their highly elliptical orbits near the Sun.
Astronomers believe there may be many more Earth-like planets with atmospheres in our galaxy and beyond, which require closer observations with telescopes like the James Webb Space Telescope and Europe’s Atmospheric Infrared Explorer telescope. More sophisticated ground-based observatories are being designed, capable of looking for chemical fingerprints in star spectra that reveal details about their composition or identify planets suitable for supporting life.
Temperature
Venus is the hottest planet in our solar system and far hotter than Earth, though not so hot that life would not exist there; Venus’ thick atmosphere absorbs solar radiation and slowly heats the planet over time, creating a greenhouse effect. Furthermore, its rotation is slower compared to the other major planets and this may be caused by its dense atmosphere acting as an anchor on its movement.
Our solar system’s other planets also exhibit similar temperature ranges, with temperatures depending on where one stands on each planet’s equator or poles. Jupiter’s equatorial region tends to be warmer due to the composition and thickness of its atmosphere; on Mars and Neptune however, their thin atmospheres prevent sunlight from reaching them directly, making their polar regions far colder than those found on Jupiter or Venus.
Telescope observations make it hard to accurately gauge a planet’s temperature; they only capture snapshots of its surface. But scientists can use orbit comparison to estimate an estimate for its average temperature – this allows them to assess whether liquid water might exist on its surface and support life there. This knowledge helps determine whether liquid water could exist on this or any other worlds where there may be life, potentially saving valuable research time by helping identify likely candidates that could support life on them.
Astronomers recently unveiled an exoplanet called Kepler-1649c that shares similar temperatures to Earth, while being situated within its star’s habitable zone. Scientists estimate this planet has an approximate surface temperature of around 290 degrees Celsius – warm enough for liquid water.
This planet is considered the closest in terms of temperature to Earth; however, other candidates exist such as TRAPPIST-1f in the TRAPPIST system, located 39 light years away with an estimated temperature of 63 degrees Celsius.
Planets in the outer solar system experience even lower temperature ranges, with Jupiter and Saturn boasting surface temperatures as low as – 234 degrees Celsius due to being further away from the sun than their four inner counterparts, thus receiving less direct sunlight on their surfaces.
Water
Astronomers have discovered a planet similar to Earth circling Proxima Centauri, the red dwarf star nearest our sun. This discovery could bring us one step closer to discovering life beyond our solar system. According to Nature magazine’s report this week, they identified this planet by following wobbles in brightness associated with Proxima Centauri that indicated there may be a planet orbiting it with liquid water — essential elements for life – in its orbit.
Proxima Centauri b, one-eighth the size of our Sun and orbiting its host star every 11 days instead of the 365-day orbit of Earth is so close to its host star that its energy supply would be less but sufficient enough for supporting an ocean on its surface.
As far away as four light years is the Sun, we cannot see its surface directly; however, its density gives away that most of its mass consists of water; only about 10% rock and 7% hydrogen or helium make up its composition (excluding gas giants such as Jupiter). Since these planets appear liquid rather than solid with low densities suggesting liquid states (liquid planets typically possess thick atmospheres rich in hydrogen that trap heat to keep themselves hot), their characteristics suggest their atmospheres probably contain thick layer of hydrogen rich atmospheres which trap heat and keep their surfaces warm over time.
Planets like these appear to be tidally locked, meaning that they always face in one direction towards their star, much like Earth does with our Moon. This could result in large oceans forming on them if their surface contains rocks; however, their atmospheres likely contain too high of pressure for complex molecules like DNA to form properly.
Scientists have also discovered evidence of water on Ceres, an icy dwarf planet larger than Earth with an ocean beneath its icy outer layer. While previously believed that Ceres was just made up of rocks, new data from Dawn shows its surface covered with salts and minerals.