18 Scorpii system is a conjectured planetary system located 45.7 light-years away in the constellation Scorpius in the caelregio Simianus. It is notable that the star at the center of this planetary system is almost identical to our Sun in many properties. This star is orbited by nearly a dozen planets, including one just like Earth.

Star Edit

18 Scorpii is a yellow main sequence star of spectral type G2Va, just like our Sun. 18 Scorpii shares many similar physical properties with our Sun, including its mass, size, luminosity, metallicity, age, and rotation. 18 Scorpii is just 129 million years younger than our Sun. At present, 18 Sco's age is identical to the Sun when dinosaurs roamed the Earth. 18 Sco is 2% more massive, 1% bigger, and 6% brighter than our Sun. It is slightly richer in metals than our Sun, but it contains three times more lithium than the Sun. Compared to the Sun's 25-day rotation, rotation period of 18 Sco is 23 days. The temperature of the photosphere of this star is 5433 K, compared to 5778 K for our star, which is really cool for a G2 star.

Planetary system Edit

Class Semimajor axis (AU) Eccentricity Orbital period (yr) Radius Mass Density (g/cm3) Gravity (g) Rotation period (d) Surface temp (K)
b LEcB 0.0697 0.00089 0.0184 0.2541 R 0.0146 M 4.984 0.226 6.7050 977
c CtEcH 0.2516 0.00275 0.1258 0.3846 R 0.0254 M 2.464 0.172 35.7511 516
d DEbH 0.4970 0.06042 0.3493 1.0875 R 0.7052 M 3.023 0.596 51.0320 701
e FEbG 0.9774 0.02210 0.9634 1.1142 R 1.4880 M 5.931 1.199 1.0590 305
f ABEaA 2.5165 0.08770 3.9801 1.5614 R 3.0075 M 4.357 1.234 0.8267 211
g ADEbA 3.3492 0.07565 6.1111 1.0075 R 1.9433 M 10.478 1.914 1.2978 201
h GJaU 10.7027 0.17052 34.9102 0.8561 RJ 5.8265 MJ 12.288 20.950 0.2700 654
i GJcP 25.2958 0.35099 126.8474 0.8414 RJ 0.1553 MJ 0.349 0.583 0.4398 64
j GJaP 39.8287 0.21500 250.6116 1.1129 RJ 2.7415 MJ 2.636 5.839 0.3924 200
k GNE 51.8102 0.05542 371.8177 0.6425 RJ 0.0974 MJ 0.488 0.624 0.5354 51
l GJbE 67.6748 0.09084 555.0710 0.9487 RJ 1.0468 MJ 1.625 3.069 0.6858 114

18 Scorpii is orbited by 11 planets, three more than in our solar system. The orbital periods range from a week to about 512 centuries and semimajor axes range from 0.07 AU to 68 AU. Planets in this system have average eccentricity of 0.1029, a bit higher than 0.0603 for our solar system.

All of the inner six planets are rocky while all outer five are gaseous or icy. The inner planets orbit up to 313 AU while the outer planets orbit at least 10.7 AU. Outer planets have higher eccentricities on average than inner planets, 0.1766 vs. 0.0416.

The planets have masses ranging from 0.015 M (little bit more massive than our Moon) to 6 MJ, varying by a factor of about 125,000. The sizes range from one quarter that of Earth (about the size of the moon) to about the size of Jupiter.

18 Scorpii b Edit

18 Scorpii b is the closest planet to the parent star at an average distance of 0.07 AU. It orbits so close to the star that it takes just 6.7 days to revolve once around the star. At this distance, the planet is tidally locked to the star, meaning its rotation period is synchronized to its orbital period. The planet has an eccentricity of only 0.00089, mostly due to tidal circulization, meaning that this planet varies in distance of only about 20,000 km, 112 times the Earth's diameter.

The innermost planet contains just 1.5% as much matter as Earth contains. The planet's diameter is 3238 km, a quarter of the Earth's size. 18 Sco b's average density is 4.89 g/cm3, which is less dense than Earth and three of four solar system's terrestrial planets. It surface gravity is 29 that of Earth's, meaning that a full-grown person would weigh just 34 pounds on 18 Sco b.

Because the planet orbits so close to the star, the surface is roasted, at the surface temperature of roughly 1300°F. At this temperature, rocks on the surface of this planet are soft. Despite the small size and mass, the planet is geologically active due to strong tidal forces of the star. Volcanoes spew out lava which cover specific areas for a long time before solidifying.

18 Scorpii c Edit

18 Scorpii c is a small planet orbiting at 0.25 AU away from the star. It is an airless crater planet with less than half the mass of Mercury. Its density is 2.46 g/cm3, suggesting that the rocky is made mostly of lighter materials, especially carbon. The planet takes over 43 days to rotate once.

18 Scorpii d Edit

18 Scorpii d is a mid-Earth with over 70% the mass of Earth and but nearly 10% larger than Earth. As a result, the rocky world is considerably less dense than Earth, 3.023 vs. 5.515 g/cm3. Its surface gravity is 60% as strong as Earth's.

This planet orbits at half the Earth–Sun distance and takes a third of an Earth year to revolve around the star. The planet takes roughly 51 days to rotate once on its axis, slightly shorter than Mercury's rotation.

18 Sco d has a thick atmosphere comprising about 95% carbon dioxide. The runaway greenhouse effect raises the surface temperature to about 800°F.

18 Scorpii e Edit

Comparing 18 Sco e vs. Earth
18 Sco e Earth
Orbital distance (AU) 0.977 1.000
Orbital period (d) 351.89 365.26
Eccentricity 0.0221 0.0167
Diameter (Mm) 14.198 12.742
Mass (M) 1.488 1.000
Density (g/cm3) 5.931 5.515
Surface gravity (m/s2) 11.75 9.80
Axial tilt 26.16° 23.44°
Rotation period (hours) 25.42 24.00
Surface temperature 90°F 59°F
Irradiance (W/m2) 1528 1368
Geometric albedo 0.308 0.367
Water proportion 26% 71%
Forest proportion 58% 9%

18 Scorpii e is a planet that is classed as an Earth analog since this rocky planet is orbiting in the middle of the habitable zone. It orbits at 0.98 AU and its year lasts 352 Earth days, and the planet makes one complete spin in 25.4 hours, compared to 24 hours for Earth. Even more friendly to Earth-like planet, this planet orbits in a circular path with an eccentricity of 0.022, only slightly higher than Earth's. In addition, this planet rotates at 24.71° relative to the orbital plane, similar to our home planet (23.44°), and with circular orbit produces Earth-like seasons.

18 Sco e masses 1.488 M and sizes 1.114 R. Its surface gravity is 20% stronger than Earth's and average density is almost six grams per cubic centimeter, denser than Earth.

Even more, the planet is surrounded by Earth-like atmosphere comprising of nitrogen, oxygen, carbon dioxide, and other gases. The average surface temperature is 90°F, a bit warmer than 59°F for Earth. The surface temperature without the atmosphere would have been 13°F, so the atmosphere must have heated by 77°F.

Most of the 18 Sco e's surface is teeming with life, the first lifeform we see are dense populations of trees. Roughly 58% of the planet's surface are covered in forests, classifying this planet as forest planet with life more diverse than there are on Earth. Water covers most of the remaining surface at 26%, while the remaining 16% are other terrain, especially deserts and mountains.

18 Scorpii f Edit

18 Scorpii f is an ammonia planet three times more massive than Earth, classifying this as super-Earth due to its mass. It orbits at 2.52 AU and takes about four years to orbit its sun. 18 Sco f's rotation period is 19 hours and 50 minutes and the planet appears orange from space with the surface temp of −80°F.

18 Scorpii g Edit

18 Scorpii g is also an ammonia planet, but orbits farther out. It orbits at an average distance of 3.35 AU and takes more than six years to make one complete trip around the star. The mass is nearly twice the Earth's, but it is about the same size, meaning its density is nearly twice that of Earth's. Its density tell that this planet has a large core made of iron and lead. 18 Sco g takes over 31 hours to make one complete spin.

On the surface, there are oceans of liquid ammonia and nitrates are abundant in minerals that make up thin crust. Below the crust and above the core is the mantle made mostly of carbon and silicates. The surface temperature is −97°F, just above the melting point of ammonia.

18 Scorpii h Edit

18 Scorpii h is a massive gas giant with mass approaching six Jupiter masses. Its orbital period is 35 years and orbits at 10.7 AU with an eccentricity of 0.17, meaning the distance varies from 8.9 to 12.5 AU. The planet's high mass would raise the temperature considerably due to internal heating it produces. The surface temp (at 1-bar layer since it has no solid surface) is 718°F. At that temperature, clouds would not form as there's no chemical suitable for the formation of clouds. 18 Sco h rotates even quicker than Jupiter, at just 612 hours compared to 10 for Jupiter.

18 Scorpii i Edit

18 Scorpii i is a gas giant contains half the mass of Saturn found at distances ranging from 16.4 to 34.2 AU throughout its 127-year orbit. Despite it's mass relative to Saturn, the planet is roughly the same size. Even though planet is 49 times more massive than Earth, its gravitational field is over 70% weaker than Earth's, so an average person would weigh just 87 pounds on 18 Sco i, compared to 150 pounds on Earth.

The planet orbits so far out that its atmosphere is frigid cold, whose temp is 344 degrees below zero, cold enough for methane clouds to form.

18 Sco i has a very high axial tilt and rotates fast. It tilts at 66° and takes more than 1012 hours to rotate once on its axis, similar to Saturn's. No other planets in this system have axial tilts greater than 26°.

18 Scorpii j Edit

18 Scorpii j is a low-mass super-Jupiter, massing at 2.74 MJ. It rotates in 9.4 hours and surface gravity is 535 times stronger than Earth's. 18 Sco j has ammonia clouds like it is found on Jupiter and Saturn with water clouds below it. Despite its mass, 18 Sco j is just 11% bigger than Jupiter due to gravitational contraction.

18 Sco j's orbital period is 212 centuries at a semimajor axis of 39.8 AU. However, the orbital distance varies from 31.2 to 48.4 AU, corresponding to its orbital eccentricity of 0.215, similar to Mercury and Pluto.

18 Scorpii k Edit

18 Scorpii k is a low-mass gas planet massing 110 that of Jupiter and sizing at 64% of that of Jupiter. The planet's density is just 58 that of water, meaning if there is ocean big enough, this planet would float. Also its gravity is weak, meaning that a 150-pound person standing on Earth would weigh just 94 pounds if standing on this planet.

18 Sco k's orbital period is 372 years and orbits at 51.8 AU in a circular orbit (e = 0.055).

18 Scorpii l Edit

18 Scorpii l is a Jupiter-size planet whose orbital period is so long that it has completed only a single orbit since pre-modern times. It takes 555 years to revolve once around the star, orbiting at 67.8 AU with an eccentricity similar to Mars' (0.091). The surface temp is 254 degrees below zero. 18 Sco l is the outermost planet in the 18 Scorpii system. Unlike its orbital period, its rotation period is not particularly long at all, completing its rotation once every 1612 hours, similar to Uranus' and Neptune's.