Kepler-90 - The latest mini-Solar System Analogue

I just saw this today, but apparently it’s month old news, so some of you may have spotted this already.

A team of European astronomers utilizing Kepler data has discovered a planetary system orbiting a Sunlike (1.1 MSun) star approximately 2500 light-years away. The system, known as Kepler-90 (or KOI-351), has at least seven planets in nearly circular orbits, and those planets are distributed in a rather Solar System-esque fashion: 3 rocky Earth-sized planets near the star, 2 “mini-Neptunes” in the mid-zone, and two gas giants in the outer regions.

This is the first large planetary system found to date with terrestrial planets found in the inner region of the system and giant planets in the outer reaches.

But here’s the kicker: The entire planetary system sits within 1 AU of the star. All seven detected planets fit at or within Earth’s orbit.

Kepler-90 h sounds very interesting from the point of view of anyone interested in looking for Earth-like moons of giant planets. With an orbital radius of 1.01 AU and an orbital period of 331 days, K90 h is a Jupiter analogue found in a nearly perfect Earth-like orbit. The planet, and any moons it may have, would receive approximately 60% more light from its star than the Earth does from the Sun (it’s actually probably a little bit less than that, as K90 is a low metallicity star, and there’s some evidence that lower metallicity stars are slightly less luminous than solar metallicity stars).

That’s a great find. It is likely for any Earth-sized moons of Kepler-90 h to be less hospitable than Earth due to higher temperatures, but it is possible that any complex lifeforms may adapt to these conditions as long as liquid water can be sustained. :smiley:

Aren’t large gas giants also prone to having strong radiation zones? Or ist that only Jupiter?

Any life that would evolve in such a zone would have an interesting evolution. Rapid changes from generation to generation, maybe naturally high radiation resistance, stuff like that. Makes me wish we could go and look… :smiley:

Jupiter has an exceptionally strong set of radiation belts, yes – on the order of a million times stronger than Earth’s radiation belts – but, much like Earth’s, their extent is limited. According to that bastion of true knowledge, Wikipedia, Jupiter’s radiation belt encompasses Io and Europa, but Ganymede appears to be situated right at the edge, and Callisto is, relatively speaking, unaffected by the radiation belts. Indeed, Ganymede appears to receive just slightly less than the amount of radiation known to cause radiation sickness; I think a larger body with a stronger internal magnetic field (i.e. an Earth-sized world) at the position of Ganymede would be able to generate its own magnetosphere and deflect the radiation from Jupiter. A planet in the position of Callisto wouldn’t even need to do that; outside the radiation belts, but protected from the solar winds by Jupiter’s magnetosphere, smaller worlds with an thick atmosphere but no magnetosphere of their own would be able to house life and still receive less than 4 rems/year of radiation, well within safety limits (the tolerance for someone working with radiation is set to 5 rem/year by the USAEC).

This gets even more favourable if we’re looking at a gas giant with a Saturn strength magnetic field, or if we’re looking at Neptunian worlds.


While more light is generally associated with higher temperatures, atmospheric and surface conditions are actually far more important, so it’s entirely plausible a moon of Kepler-90h could have Earth-like temperatures. The obvious example of this effect is to compare the temperatures of Venus and Mercury (spoiler: Venus is hotter, Mercury is almost twice as close to the Sun).

As for whether it’d have an Earth-like climate is an entirely different issue - apart from the obvious tidal effects of orbiting a gas giant, the reflected light from a planet the size of Jupiter, getting more light than the Earth, could have some interesting effects on global climate when passing between it and the star.

Oh and btw, an entire Sol-like system sitting within 1AU of it’s star? I hereby rename Kepler-90 to the Kerbol System. Squad just needs to add a couple of planets to the game (Kerbal Space Program).


I second this motion.

Unlike Venus, of course, Mercury has no atmosphere to insulate that heat.
Kerbol in KSP is actually colder than Sol… but at least Laythe is a bit hotter (and fits right in :smile: )