Hacker News Reader

Comment by jpreiland | Hacker News Reader

To rephrase another comment in the other submission - how do we know/can we infer so much about a planet so far away when we are just now getting reasonable pictures of Pluto?

Looking at the images (aside from the artist interpretation), it looks like they're just guessing based on size and location?

View on HN

One thing to keep in mind is that there is one thing that happens with exoplanets that can never happen with Pluto: the planet can pass between its star and us (i.e. eclipse the star). This gives a lot of information about the planet's composition, because light from the star will scatter/change color according to the planet's composition. See this image: http://seagerexoplanets.mit.edu/images/transitschematic.gif.

Now maybe you can do that with Pluto using some far-off star for reference, not sure. Also, I'm not sure if in this specific example the exoplanet made a transit of its star, or if it was detected by other means (usually by measuring its gravitational affect on the star, i.e. its star "wobbles").

> Now maybe you can do that with Pluto using some far-off star for reference, not sure.

It has been done for Pluto, first in 1988, with an occultation of a background star[0].

[0] http://www.space.com/29885-pluto-atmosphere-to-be-revealed-b...

And most recently with SOFIA at the end of June:

https://sofia.usra.edu/News/news_2015/06_29_15/index.html

This will help tie in past and future occultation observations to the New Horizons data.

As I understand, star transits by Pluto helped to better estimate its size before NH. But as you said, it's complicated to get a full spectrographic analisys of its atmosphere this way.

Kepler is a mission that mostly works with photometric measurements of planet transits in front of their stars.

And indeed the fact that the observed transits were "fuzzy" told us that Pluto has a (very tenuous) atmosphere. Indeed, Pluto's diameter had considerable uncertainty before New Horizons arrived due to this (unlike Charon's whose transits were always tack sharp.)

Indeed this is exactly what New Horizons did very recently. After shooting past Pluto, the probe spun around to view it with the sun behind it. http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?...

We had a good idea of what pluto looked like for decades. But no photo to confirm; the fact it was red, rocky, pocked, etc. We know characteristics about distance, composure, mass, energy, etc. using spectroscopic techniques. Those spectroscopic techniques are applicable to those planets way out there as well.

I believe they're basing it on size, temperature, and the assumption that the planet is rocky.

Sounds like age, size, density/mass, orbit/location

Reply on news.ycombinator.com