55 Cancri e

55 Cancri e / Janssen
Artist's impression of 55 Cancri e near its host star
Discovery[1]
Discovered byMcArthur et al.
Discovery siteTexas, United States
Discovery date30 August 2004
Radial velocity
Orbital characteristics
Apastron0.01617 AU (2,419,000 km)
Periastron0.01464 AU (2,190,000 km)
0.01544 ± 0.00005 AU (2,309,800 ± 7,500 km)[2]
Eccentricity0.05 ± 0.03[3]
0.73654625(15) d[4]
17.67711 h
Inclination83.59 +0.47
−0.44[3]
2,449,999.83643 ± 0.0001[5]
86.0 +30.7
−33.4[3]
Semi-amplitude6.02 +0.24
−0.23[3]
Star55 Cancri A
Physical characteristics
1.875 ± 0.029[3] R🜨
Mass7.99 +0.32
−0.33[3] ME
Mean density
6.66+0.43
−0.40[3] g cm−3
2.273 g
Temperature3,771+669
−520 K (3,498 °C; 6,328 °F, dayside)[6]
<1,649 K (1,376 °C; 2,509 °F, nightside)[6]

55 Cancri e (abbreviated 55 Cnc e, also known as Janssen /ˈdʒænsən/) is an exoplanet orbiting a Sun-like host star, 55 Cancri A. The mass of the exoplanet is about eight Earth masses and its diameter is about twice that of the Earth.[3] 55 Cancri e was discovered on 30 August 2004, thus making it the first super-Earth discovered around a main sequence star, predating Gliese 876 d by a year. It is the innermost planet in its planetary system, taking less than 18 hours to complete an orbit. However, until the 2010 observations and recalculations, this planet had been thought to take about 2.8 days to orbit the star.[5]

Due to its proximity to its star, 55 Cancri e is extremely hot, with temperatures on the day side exceeding 3,000 Kelvin.[6] The planet's thermal emission is observed to be variable, possibly as a result of volcanic activity.[7] It has been proposed that 55 Cancri e could be a carbon planet.[8]

The atmosphere of 55 Cancri e has been extensively studied, with varying results. Initial studies suggested an atmosphere rich in hydrogen and helium,[9] but later studies failed to confirm this, instead supporting an atmosphere composed of heavier molecules,[10] possibly only a thin atmosphere of vaporized rock.[11] Most recently as of 2024, JWST observations have ruled out the rock vapor atmosphere scenario and provided evidence for a substantial atmosphere rich in carbon dioxide or carbon monoxide.[12]

  1. ^ Cite error: The named reference McArthur2004 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference rebekah10 was invoked but never defined (see the help page).
  3. ^ a b c d e f g h Cite error: The named reference Bourrier2018 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Kokori2023 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference fischer08 was invoked but never defined (see the help page).
  6. ^ a b c Cite error: The named reference Mercier2022 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference 2016MNRAS.455.2018D was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference thatgoofydiamondarticle was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Tsiaras2016 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Zhang2021 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Rasmussen2023 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Hu2024 was invoked but never defined (see the help page).