Star may have drawn scorching 'hell planet' into super-close orbit

An artist's depiction of the "hell planet" Janssen orbiting its star.
An artist's depiction of the "hell planet" Janssen orbiting its star. (Image credit: Lucy Reading-Ikkanda/Simons Foundation)

You thought Venus was hot? 

While the planet does have an average surface temperature of nearly 900 degrees Fahrenheit (500 degrees Celsius), there's an exoplanet just 40 light-years away from Earth that has a surface temperature a scorching three times hotter: 3,600 degrees Fahrenheit (2,000 degrees Celsius). Now, new data has led scientists to develop a theory of how this "hell planet" came to be. 

With a mass about eight times that of our planet, the rocky exoplanet 55 Cancri e (shortened to 55 Cnc e and formally called Janssen) is considered a super-Earth, but its surface conditions couldn't be more different from those we enjoy. Janssen orbits its star, called 55 Cancri or Copernicus, at a distance of just 1.4 million miles (2.4 million kilometers), making the planet's year just 18 hours long. By comparison, Mercury orbits about 36 million miles (58 million km) away from the sun. That proximity, of course, is what makes 55 Cancri e so hot — hot enough that the surface of the planet is an ocean of lava and its interior may be filled with diamonds.

Related: 7 ways to discover alien planets

Because of Janssen's tight orbit, astronomers have had difficulty studying the planet. But using data from the new Extreme Precision Spectrometer (EXPRES) at the Lowell Observatory's Lowell Discovery Telescope in Arizona, astronomers have for the first time been able to determine the planet's orbital plane, influencing their theory for how the planet formed.

Unlike the other planets in the system, Janssen orbits around Copernicus' equator. Researchers now believe the planet initially formed in a more distant — and thus cooler — location, then was later pulled into its current orbit by Copernicus' gravity.

"We've learned about how this multi-planet system — one of the systems with the most planets that we've found — got into its current state," Lily Zhao, an astrophysicist at the Flatiron Institute in New York and lead author of a new study on the observations, said in a statement.

The research into Janssen could unveil new discoveries about the formation and movement of planetary systems, which in turn could help scientists determine whether or not life might exist elsewhere in the universe. And that's exactly what the team plans to study next.

"We're hoping to find planetary systems similar to ours and to better understand the systems that we do know about," said Zhao.

A study describing the team's research was published Thursday (Dec. 8) in the journal Nature Astronomy.

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Stefanie Waldek
Contributing writer contributing writer Stefanie Waldek is a self-taught space nerd and aviation geek who is passionate about all things spaceflight and astronomy. With a background in travel and design journalism, as well as a Bachelor of Arts degree from New York University, she specializes in the budding space tourism industry and Earth-based astrotourism. In her free time, you can find her watching rocket launches or looking up at the stars, wondering what is out there. Learn more about her work at

  • rod
    Some other reports are out on this exoplanet now too.

    How the 'hell planet' got so hot: New measurements reveal the orbital path of planet 55 Cnc e,
    My note. This is a five-exoplanet system where the planets do not orbit around the host star in a flat plane. 55 Cnc e seems to do this, the other four are exceptions. Planet migration scenarios are used to explain the present orbit of 55 Cnc e.

    ref - Measured spin–orbit alignment of ultra-short-period super-Earth 55 Cancri e,, 08-Dec-2022. “Abstract A planet’s orbital alignment places important constraints on how a planet formed and consequently evolved. The dominant formation pathway of ultra-short-period planets (P < 1 day) is particularly mysterious as such planets most likely formed further out, and it is not well understood what drove their migration inwards to their current positions..."

    My note. "The spin–orbit alignment of 55 Cnc e favours dynamically gentle migration theories for ultra-short-period planets, namely tidal dissipation through low-eccentricity planet–planet interactions and/or planetary obliquity tides." My note, gentle migration theories. 55 Cnc e is documented at

    This is a five-exoplanet system. Using properties at for 55 Cnc e I calculate P = 6.9550E-01 day or 0.6955 day. The published value = 0.7365478 day. In 1 Gyr, 5.2516E+11 revolutions could be completed or more than 525 billion revolutions. The host star is said to be 10.2 Gyr old. More than 5 trillion revolutions now. Apparently, some type of gentle migration scenario is required to explain this exoplanet and five planet system.

    Observing trillions of revolutions around the host star - looks difficult :)
  • rod
    Exoplanet studies now are very interesting. Here is a new report on exoplanet masses and densities using 10^6 number in simulations. Efforts to quantify mass, density, and radius, exoplanets with radii 2 or less earth radii.

    The Nominal Range of Rocky Planet Masses, Radii, Surface Gravities and Bulk Densities,
    My notes. From the 41-page PDF report. “1. INTRODUCTION The compositions of small (R <= 2Rearth) exoplanets provide considerable information about their formation (e.g., Unterborn et al. 2018a; Adibekyan et al. 2021), interior dynamics (Ballmer et al. 2017; Spaargaren et al. 2020), and potential habitability (e.g., Unterborn et al. 2022). Attempts to quantify the composition of small exoplanets has been ongoing for over a decade, by attempting to match a planet's measured density to those predicted by mass-radius models (e.g., Valencia et al. 2006; Seager et al. 2007; Valencia et al. 2007a,b; Zeng & Seager 2008; Dorn et al. 2015; Unterborn et al. 2016, 2018a; Huang et al. 2022). Recent work has used mass-radius modeling to identify high-density super-Mercuries (e.g., Bonomo et al. 2019) as well as small planets that contain significant surface water (e.g., Unterborn et al. 2014) or thick atmosphere (e.g, Brinkman et al. 2022), which lower their bulk densities considerably, making them water-worlds and mini-Neptunes, respectively.”

    "Table 1. Sample of planets with uncertainties less than 30% in both mass and radius with the highest and lowest likelihood of being in NRPZ"

    "Table 2. Sample of well-characterized exoplanets with available host-star abundances. Host star elemental ratios are expressed as molar ratios derived using the solar abundances of Lodders et al. (2009). All masses and radii taken from the NASA Exoplanet Archive (Akeson et al. (2013), 10.26133/NEA1) and stellar abundance data are from the Hypatia Catalog. The classifications in the last column are illustrated in Figure 21, where SM = Super-Mercury, and IHS = indistinguishable from host star. CMF values correspond to the median values and 1sigma confidence intervals"

    Another note I make, presently 133 exoplanets have atmospheres studied and listed, This is another critical parameter when thinking about if any exoplanets are earthlike.

    The NASA exoplanet archive site presently shows 1474 exoplanets with radius 2 or less earth radii.
    NASA Exoplanet Archive (
    The site shows 1404, The Extrasolar Planets Encyclopaedia (
    Exoplanet studies like this raise questions about are there indeed, habitable earthlike planets out there? Knowing and confirming specific properties of exoplanets is required to answer. Astrobiology at some point, must show biological life exists, somewhere other than here on Earth and abiogenesis doctrine for the origin of life on Earth needs this too.