Gliese 1002

h/t Nyrath the 1002 entry in the Gliese catalogue has planets. Two of them - Earth-sized (at least), habitable-zone. This star has a whopping triple-digit parallax setting it at a mere 15.8 light years away.

These were found by Canary Island 'scopes, hence the peacocking by the IAC. Gliese 1002 is dim, weighing in at 0.120±0.010 M_☉ (39954 M_⊕). It is no flare star, either; which was nice for the observers. They assume older than Proxima 4.85 Gyr.

Springing out to me, the planets run in a 2:1 resonance like Io and Europa, like Europa and Ganymede. Inner planet goes around ten-ish days more precisely 248 hours and maybe ten minutes. Compare Io 42.5 hours - so, b takes 5.839 times longer than that, more like a Ganymedean orbit.

But the innermost's 10.35 days doubled doesn't quite hit the 21.2 days of the next one out. The mean-motion equation n_b - 2n_c is, in degrees, 360 / 10.3461 - 2 * 360 / 21.202 = 0.83666 °/day; compare Io/Europa 0.7395 °/day. Although it's less a proportion of n_c = 16.97953 °/day than what Io/Europa got against Europa. I'll get back to this.

These aren't transits so the masses are minima: in from out they are 1.08 ± 0.13 M_⊕ and 1.36 ± 0.17 M_⊕ sin i. Mass-ratios against their sun would be 2.7031e-5 and 3.4039e-5, a reverse of the Io/Europa range 4.497e-5 and 2.536e-5 (respectively). The researchers aren't hazarding inclinations relative to Earth. I'd hoped we've the stellar inclination, for a red-dwarf, but nobody's bothered measuring GJ 1002's. Although they did get a rotation, 126±15 days; implying the angle isn't too edge-on.

So I'll papernapkin this, with Hill Spheres. Based on that Keplerian mass a³/T²= 8.9416038541891E-07, our boy Johnny says 0.0457 AU and 0.0738 AU (again, no direct imaging). If they were edge-on 90° to us and if the errors be all zero, which they are not, the zones-of-influence are 0.00095 L2 against 0.0016 L1. So: the outer planet reaches only to 0.02715 AU. That is: boosting the latter to 6 M_⊕ (sin i = 1.36/6; i = 0.2286539 rad = 13.1°) would overlap its L1 into the inner L2.

Personally I doubt we're expecting 13.1°. It's all more likely less perpendicular to us.

The planets' rotations've got to be tidally-locked, both of them.

We don't know if Gliese 1002 hosts anything as rocks a five day orbit, or 20/3 days. Mind, for any such conjectures we must impose mass constraints. I suspect such would have shown up in the data unless it were very much less massive than the other two.

REPOST: I'd done a lot of it yesterday evening but, on further review, the title and conclusion were too unfocused. Here's the new followup.

IT'S COLD OUT THERE 2/18/23: The inner planet at 67% irradiance looks Huronian like Wolf 1069's, albeit maybe rockier. The outer one at 26% is a superCeres or even Hycean.