Voyage to Planet Nine

[LongTomH]

The Centauri Dreams blog can be a fun place to visit; subject range from planetary science to Search for Extra-Terrestrial Intelligence to interstellar travel. Their most recent post is speculation on missions to the hypothetical 'Planet Nine' way out in the 'burbs of the solar system. The author, Adam Crowl is a member of the Icarus Interstellar project to redesign the Daedalus interstellar probe, proposed by the British Interplanetary Society in the late '70s.

In The Snowbank Orbit, Redux, Adam speculates about the hypothetical planet and how a future mission might not only reach the planet, but go into orbit around it:

Fritz Leiber is better known for his fantasy and SF-fantasy, but he could write hard-SF too. A fine example is his 1962 story, “The Snowbank Orbit”, the title of which alludes to World War II tales of pilots surviving bailouts without parachutes by plunging into snow-drifts. Five spacecraft, racing towards Uranus at 100 miles per second with empty tanks, intend a fiery plunge through the planet’s atmosphere to brake into orbit. The rest of that story I will leave to the interested reader (available here) but the idea of aerobraking into orbit around a distant Planet Nine is worth discussing.

Presently we know very little about Telisto – the mellifluous name suggested for Planet Nine by physicist Lorenzo Iorio [1] which I’ll use for convenience. Brown & Batygin [2] suggest an orbit averaging about 700 AU and a mass of at least 10 Earth masses. The mass could be somewhat higher, though certainly not of the order of a Saturn-mass as its infra-red glow would’ve been seen by earlier surveys. Modelling [3] suggests a 10 Earth-mass planet, with a substantial hydrogen-helium envelope, could be as ‘warm’ as 50 K – about 40 degrees warmer than the ~10 K from sunlight alone. A range of compositions were modelled. A Super-Earth, an Ice-Giant (like Uranus/Neptune) and a miniature version of Jupiter/Saturn are all possible. Some cosmogonic simulations [4] suggest a Neptune like object is likely to have been flung from amongst the other giant planets during their formation, so it seems the most likely option.

A Neptune-like Telisto would then be an ice-wrapped rocky core wrapped in a layer of captured hydrogen/helium mixture. It’s likely that hydrogen will be depleted from its atmosphere by some fraction being chemically bound and mixed with its core, so helium will be a higher fraction of the atmosphere, as appears to be the case for Neptune. If the atmosphere is a small fraction of Telisto’s mass, then it’s possible it will have an icy surface or even a liquid water ocean under a hydrogen atmosphere via its greenhouse effect trapping the planet’s internal heat. In that case Telisto will be very interesting from an astrobiological perspective, though the energy sources available to sustain life are impossible to quantify at present.

Adam, and others, are already thinking about how a future probe might reach Tellisto and set up orbit around it.

Deep Space Propulsion

Given sufficient motivation we’ll send a probe and eventually follow in person. Getting there will be a challenge. At the present 3.5 AU/year of “Voyager 1” the journey would take 200 years. Leiber’s 100 miles per second would get a probe there in 20 years, which might be acceptable if the probe has a compelling secondary mission it can pursue during the long cruise phase. Long baseline telescopic observations might be sufficiently attractive to combine the two. A flyby at 100 miles per second is probably too quick to provide sufficient science return for the investment, so stopping will be required.

The article discusses various means of propulsion, including ion engines powered by advanced forms of nuclear reactors and various sails: lightsails, 'e-sails' and magsails. I'm disappointed that Adam didn't include the VASIMR (Variable Specific Impulse Magnetoplasma Rocket engine), which might have advantages over ion engines.

Adam suggests the proposed Telisto probe use a aerobraking to slow enough to enter orbit around the planet.

[muriel_volestrangler]

1. That's an awful suggestion for the name

Unlike all the planets/dwarf planets/KBOs etc. that have already been named, it's not from any mythology - it just seems he suggested it because it's far away, and has 'tel' in it, the Greek for 'far'.
http://adsabs.harvard.edu/abs/2015arXiv151205288I

Telisto is actually a brand of iced tea: https://www.caloriecount.com/calories-mccormick-telisto-light-limon-i411667

and it sounds almost identical to Telesto, an existing moon of Saturn, which is named after a character from Greek mythology:

https://en.wikipedia.org/wiki/Telesto_%28moon%29

[Lorenzo Iorio]

3. Why Telisto?

Hello. The name I proposed comes from the Greek word τήλιστος (télistos), meaning "farthest, most remote"
[link:http://www.perseus.tufts.edu/hopper/morph?l=th%2Flistos&la=greek&can=th%2Flistos0&prior=pera/th|
In my view, it is better suited than Planet Nine since it captures an essential feature of this hypothetical planet, i.e. its large distance from the Sun, which will not be changed by any further discovery about it (if it really exists, of course), and is independent of any classification schemes.

Telesto has a quite different origin: it is the name of a deity of the Greek mythology, i.e. Τελεστώ (Telestò)

[LongTomH]

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Edited to add: Lorenzo Ioro is the physicist whose work on orbits of Kuiper Belt Objects (KBO) predicted a ninth planet about 700 AU out from the sun, as well as the person who suggested the name: Telisto

[Javaman]

2. Plan-et Nine from Outer Space. nt