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Entering orbit…
Habitability
17/ 100
Uninhabitable
HD 40307 e rendered in TerraForge from its measured mass, orbit and star

HD 40307 e

Also written HD 40307e

Sub-NeptuneUninhabitable42 light years awayFound 2012
exoplanet.euListed by the Extrasolar Planets Encyclopaedia; not yet in NASA's confirmed catalogue.View on exoplanet.eu

Estimated: this planet doesn't transit its star, so its size is inferred, not measured

HD 40307 e, from the Extrasolar Planets Encyclopaedia (found 2012). Measured: 3.5 Earth masses, 0.189 AU, a 4977 K K-type star. Composition inferred from a estimated bulk density of 0.73x Earth's, modeled rather than measured since this isn't a transiting planet, too low for bare rock at this size, suggesting a rocky core under roughly a 0.9% hydrogen/helium envelope by mass, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Host star

HD 40307

Type
K-type (Orange)
Spectral type
K2.5V
Temperature
4,977 K
Mass
0.77 ☉
Known planets
6, including this one

Published by the Extrasolar Planets Encyclopaedia. This star’s luminosity has not been published, so this world’s temperature and habitability score fall back to a typical K-type star.

Gas Dwarf

Life unlikely — too hot for liquid waterMagnetic FieldLow Activity
Why is this a Gas Dwarf?
HD 40307 e has an unusual composition that doesn't fit standard classifications, or lacks the elements needed for complex geological processes.
Barren worlds can form from uncommon element combinations or may be remnants of larger bodies that lost their atmospheres and volatile materials.
Classification Criteria:
Composition doesn't match standard planet typesMass: 3.5x EarthTemperature: 516K

Reading HD 40307 e’s atmosphere

Dominant elements: O, Si, Fe, N, C, HThis is what a telescope would measure while HD 40307 e crosses in front of its star: starlight passes through the atmosphere and spreads into a rainbow band. Each dark line marks a wavelength the atmosphere absorbed.Every element absorbs its own signature wavelengths — hydrogen always darkens the same two spots, calcium another pair, and so on. Astronomers match the lines in a real spectrum against a library of these signatures to say what an atmosphere is made of, light-years away, without ever visiting. A deeper line generally means more of that element is present.HD 40307 e sits about 42 light-years away, found by the radial velocity method. Most catalogued distances trace back to parallax: as Earth orbits the Sun, a nearby star appears to shift very slightly against the distant background stars, and the size of that shift gives its distance directly.
Further reading
ExoplanetsSara Seager (editor)The field's standard reference: how planets are found, how they form, and what their atmospheres are made of.The Planet FactoryElizabeth TaskerHow planets are made, and why so few of them come out like Earth.Exoplanets: Diamond Worlds, Super Earths, Pulsar PlanetsMichael Summers & James TrefilThe strange end of the catalogue — carbon worlds, molten rock, planets orbiting dead stars.The Little Book of ExoplanetsJoshua WinnHow these worlds are found, and what a measurement can honestly tell us.
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Habitability ScoreUninhabitable
17
Contributing Factors
temperature15
Extremely hot - hostile to known life forms
atmosphere30
Hydrogen-rich atmosphere typical of gas giants
water15
No solid surface — any water is locked in a supercritical mantle and hot ice, not oceans
magnetic Field100
Magnetic field provides radiation protection
geology60
Some geological activity provides slow nutrient cycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
3.50x Earth (2.09e+25 kg)
Radius
1.52x Earth (9,673 km)
This planet: 1.52× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.52x Earth (14.9 m/s²)
Surface Temperature
516 K (243 °C / 469 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Orbital Environment

Star Type
K-type (Orange)
Distance from Star
0.19 AU (28.3 million km)
Orbital Period
36 days

Atmosphere

Deep hydrogen-helium envelope with photochemical haze

Elemental Composition

O - Oxygen
31.3%
Si - Silicon
25.0%
Fe - Iron
12.5%

Surface Characteristics

No solid surface - a hydrogen-helium envelope wrapped around a rocky core (a sub-Neptune)
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The surface of TOI-700 d as TerraForge draws it: red-leaved trees over green ground under a lavender sky

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