HR 8799 d
HR 8799 d
confirmed planet • updated: 2014-05-14
HR 8799 d was one of the first planets ever directly photographed. It orbits a bright, young star and was spotted using powerful telescopes on Earth, including the Keck Observatory.
This page summarizes a catalog entry. If a measurement is missing, it is not shown or guessed. Some values can differ slightly between studies; when that happens, we describe the range rather than picking a favorite without evidence.
Scientific context
Scientific context: This profile layers interpretation on top of archival measurements. Modeled bands appear where direct detections (like spectra or transits) are not listed.
What we can’t claim: surface conditions, biology, or breathable atmosphere without direct spectra.
HR 8799 d is a massive planet, about 10 times the mass of Jupiter, with a radius roughly 1.2 times Jupiter’s. It orbits its star at a distance of about 24 astronomical units (AU), taking roughly 37,000 Earth days (about 100 years) to complete one orbit. Because it was directly imaged, scientists can estimate its mass and size more directly than with other methods, though some details like orbital eccentricity or exact temperature are not listed here.
Glossary (plain English)
- AU: the average Earth–Sun distance.
- Semi-major axis: the planet’s average distance from its star.
- Eccentricity: how oval the orbit is (0 = circle).
- Radial velocity: finding a planet by measuring a star’s tiny “wobble.”
- m·sin i: a minimum mass estimate; the true mass can be higher if the orbit is tilted.
- Equilibrium temperature: a rough estimate from starlight alone, not a surface reading.
HR 8799 d was first reported in 2008 using the Imaging method. The discovery is linked to observations from W. M.
Keck Observatory. Direct imaging tries to separate faint planetary light from the glare of the host star. It works best for young, warm planets far from their stars.
The catalog lists an orbital period of about 37000.00 days, a semi-major axis near 24.000 AU.
Eccentricity is not provided here; many catalogs omit it when the solution is underconstrained. Because this is a multi‑planet system, stability is ultimately tested with dynamical (N‑body) fits; catalogs can update as models improve.
The archive reports a mass scale of 10.0 MJ.
A catalog radius is also listed, which (together with mass) helps constrain density and interior structure.
Why “m·sin i” shows up on RV planets
HR 8799 d orbits HR 8799.
The star is classified as A5 V, which is a shorthand for temperature and color. The system is about 134.5 light‑years away.
Several key parameters are not present in this single catalog row. Missing fields don’t mean the science is unknown—only that this particular snapshot doesn’t carry the values.
In this case the most noticeable gaps are: catalog equilibrium temperature, eccentricity. As new observations arrive, archives often refresh these entries (and sometimes revise earlier numbers).
Scientists keep revisiting systems like this because each new instrument pass can tighten uncertainties: better timing improves the orbit, better spectra improves the star, and better follow‑up can confirm or refute competing solutions. Even when a planet is well‑established, refined stellar properties can shift the inferred planet size, temperature, and habitability context.