For centuries, humans have wondered if there are other planets like Earth in the universe that could potentially harbor life. With the discovery of thousands of exoplanets in recent decades, astronomers have found several planets outside our solar system that have characteristics similar to Earth. But which of these planets is the most Earth-like and closest to our home planet? In this article, we will examine some of the top contenders for the closest Earth-like exoplanet and look at how they compare to our own planet.
What makes a planet Earth-like?
When searching for Earth-like planets, astronomers look for planets that meet several criteria:
- Located in the habitable zone of its star – The habitable zone, also called the “Goldilocks zone,” refers to the area around a star where liquid water could exist on a planet’s surface. This liquid water is considered essential for life as we know it.
- Rocky terrestrial planet – Planets must be rocky like Earth, not a gas giant like Jupiter. Rocky planets up to about 1.5 times Earth’s size are believed to be most promising for habitability.
- Orbits a sun-like star – The host star needs to be a main-sequence star like our sun. Red dwarf stars are now considered possible candidates but were initially ruled out.
- Comparable size to Earth – A planet should be 0.5 to 1.5 times Earth’s size to be potentially habitable.
- Similar temperature conditions to Earth – Average surface temperatures estimated from -40°C to +30°C (-40°F to 86°F).
The more features a planet shares with Earth, the more “Earth-like” it is considered by astronomers. However, some of these criteria carry more weight than others in the search. The location in the habitable zone and rocky composition are considered the most critical factors. Even if a planet meets the size and temperature requirements, it would not be able to sustain life if it lies outside the habitable zone or is a gas giant rather than terrestrial.
Top Contenders for Closest Earth-like Planet
Several exoplanets discovered in the last decade rank among the most promising candidates for being Earth-like and relatively close to our solar system. Here are some of the top contenders:
Proxima b
- Distance from Earth: 4.2 lightyears
- Host Star: Proxima Centauri (red dwarf star)
- Size: 1.17 times Earth’s size
- Orbit: Within habitable zone
- Temperature Estimate: -40°C to +30°C (-40°F to 86°F)
Proxima b orbits in the habitable zone of Proxima Centauri, the closest star to our sun at just over 4 lightyears away. Discovered in 2016, Proxima b is close to Earth’s size and estimated to have comparable temperatures. However, there are several challenges to habitability. As a planet around a red dwarf star, it is subject to more radiation and stellar flares. Proxima b is also likely tidally locked with a permanent day and night side. Despite the challenges, Proxima b remains one of the best candidates for being an Earth-like planet relatively nearby.
Ross 128 b
- Distance from Earth: 11 lightyears
- Host Star: Ross 128 (red dwarf)
- Size: 1.35 times Earth’s size
- Orbit: Within habitable zone
- Temperature Estimate: -60°C to +20°C (-76°F to 68°F)
Ross 128 b was discovered in 2017 and orbits a quiet red dwarf 11 lightyears away. It is similar in size to Earth and resides in the temperate habitable zone. However, Ross 128 emits less radiation and is more stable than Proxima Centauri, making it possibly a more favorable environment. The estimated equilibrium temperature range of Ross 128 b is also closer to Earth’s average. The planet is a leading candidate for habitability among the red dwarf star systems near our solar system.
Teegarden b
- Distance from Earth: 12.5 lightyears
- Host Star: Teegarden’s Star (red dwarf)
- Size: 1.05 times Earth’s size
- Orbit: Within conservative habitable zone
- Temperature Estimate: +5°C to +23°C (41°F to 73°F)
Teegarden b was discovered in 2019 and is one of two planets orbiting the nearby red dwarf Teegarden’s Star. At just over 1 Earth mass, it is very similar to Earth in size and is right in the middle of the habitable zone with estimated temperatures more Earth-like than many other candidates. Its star is quiet and stable as well. However, as with all red dwarf planet candidates, there are concerns about tidally locked rotation and higher radiation levels. But Teegarden b joins the ranks of one of the most potentially Earth-like planets found to date.
Comparison to Earth
Here is a comparison of how some of these top contenders stack up to Earth:
| Planet | Distance (lightyears) | Star Type | Planet Size | Orbit in Habitable Zone | Estimated Temperature Range |
|---|---|---|---|---|---|
| Earth | – | G-type Main Sequence | 1 Earth radius | In habitable zone | -15°C to +35°C (5°F to 95°F) |
| Proxima b | 4.2 | M-type Red Dwarf | 1.17 Earth radius | In habitable zone | -40°C to +30°C (-40°F to 86°F) |
| Ross 128 b | 11 | M-type Red Dwarf | 1.35 Earth radius | In habitable zone | -60°C to +20°C (-76°F to 68°F) |
| Teegarden b | 12.5 | M-type Red Dwarf | 1.05 Earth radius | In habitable zone | +5°C to +23°C (41°F to 73°F) |
As the table illustrates, while the exoplanet contenders have some similarities to Earth, notable differences exist as well. However, they currently rank as some of the most Earth-like based on their size, estimated surface temperatures, and location in the habitable zone.
Challenges in Finding Earth’s Twin
While planets like those described above are considered Earth-like and potentially habitable, astronomers also acknowledge the challenges in finding a true Earth analogue. Some of the key complicating factors include:
- Limited technology & observational capabilities – Current telescopes and instruments are only able to detect large exoplanets relatively close to Earth. Smaller, more distant planets are difficult to detect.
- Unknown planetary characteristics – Detailed atmospheric composition, geology, and other factors remain unknown for most exoplanets.
- Differences in host stars – Red dwarfs pose challenges like stellar flares and tidal locking that may limit habitability.
- Too hot or too cold – Many otherwise Earth-like planets have estimated temperatures above or below the range needed for liquid water.
- Not a terrestrial planet – Exoplanets observed to be Earth-sized are often gas planets rather than rocky planets.
Overcoming these obstacles will take more advanced telescopes and instruments that allow the atmospheres, geology, and other characteristics of smaller, more distant exoplanets to be analyzed. But the rapid pace of exoplanet discovery gives hope that a very Earth-like planet may be identified before too long.
Future Outlook
What are the prospects for finding a planet that truly matches Earth in the future? There are several promising astronomy missions and new telescopes coming soon that will advance the search:
- James Webb Space Telescope – Launching in 2021, Webb will be able to characterize exoplanet atmospheres and acquire infrared spectra from promising planets.
- PLATO – This ESA mission launching in 2026 will detect and characterize rocky planets around sun-like stars.
- Nancy Grace Roman Space Telescope – NASA’s upcoming space observatory could discover thousands of new exoplanets using microlensing and precision measurements.
- Extremely Large Telescopes – Ground telescopes like the ELT, TMT, and GMT coming in the 2020s will allow detailed exoplanet characterization.
With these and other missions on the horizon, astronomers are optimistic about identifying even more Earth-like worlds and possibly life beyond our solar system. The closest, most Earth-like planets like Proxima b and Ross 128 b provide exciting targets for observation by advanced future telescopes.
Conclusion
The search for Earth 2.0 is an ongoing quest in astronomy and astrobiology. While no planet found to date perfectly matches our home planet, advances in exoplanet detection and analysis have uncovered several promising candidates for being Earth-like. Planets like Proxima b, Ross 128 b, and Teegarden b currently rank among the most similar to Earth in size, estimated surface temperature, and location in the habitable zone. However, notable differences between Earth and these worlds also exist that illustrate the challenges in finding Earth’s true twin. Upcoming telescopes and space missions provide hope that an even more Earth-like planet may be identified in the not-too-distant future. For now, these few worlds represent our best candidates for an Earth analogue that may possibly harbor life outside our solar system.