Freitag, 28. März 2014

GreWi-Interview: Scott S. Sheppard on the discovery of the new far out dwarf planet in our solar system and its implications

Diagram showing the orbits of dwarf planet Sedna (orange) and the new discovered "2012 VP113" (red) surrounding the solar system's center with the known planets (pink) and the Kuiper-belt (green). | Copyright/Source: Scott S. Sheppard/Carnegie Institution for Science

Saarbrucken (Germany) - The discovery of a second far out dwarf planet at the outermost edge and beyond our known solar system, as it was reported last Wednesday by astronomers of the Carnegie Institution for Science draws a new picture of our very own home planetary system. The editor of the German frontier-science news-blog "" (GreWi), Andreas Mueller, interviewed Scott S. Sheppard - one of the discoverers of "2012 VP113" - on it's discovery and in far reaching implications.

GreWi: Dear Mr. Sheppard, your discovery of a second dwarf planet like Sedna is already an amazing discovery. However, the implications it raised and which you describe in your paper sound even more fascinating. Did I understand it correct, that you estimate that there are about 900-1000 more of such large - and even larger – bodies, some that might be as big as our planet Earth?

Scott S. Sheppard. | Copyright/Quelle:
Sheppard: Yes, there are a lot of large objects in this distant region. The objects are so distant that even Earth sized objects would not have been detected to date because we have not much of the sky to the faint levels needed to find these objects. We have only searched about 5 percent of the sky to date for faint distant objects, so that leaves a lot of sky out there were large objects can be found.
GreWi: And this is also why we are able to discover planets around other far away stars (exoplanets) but do know that little about our very own planetary backyard of our solar system?
Sheppard: Yes. We use different techniques to find planets in our own solar system versus other solar systems. We detect objects by reflected sun light in our solar system, just like we see the moon, by reflected sun light. When objects are very far out they receive very little sun light to reflect and thus they are very, very faint. Exoplanets are discovered not by reflected sun light, but by gravitational wobbling of the star, which requires a very large planet to detect this or by a planet moving in front of its star and thus blocking starlight. These techniques cannot be used in our own solar system to find planets.
GreWi: If we will find such objects (as big and even bigger than Earth), would they be characterized as "planets" according to the standards of the International Astronomical Union (IAU)?
Sheppard: This is a good question. An object must satisfy three criteria to be called a planet:
1. It must orbit the Sun.
So all these objects would satisfy that.

2. It must be massive enough that gravity will shape it into a sphere.

That would also be the case for these very large objects in the outer solar system.

3. It must clear its orbit of other objects.

This would not be the case, even for a Earth sized planet, as there are many other objects in this area. So it would be a strange situation to have an Earth sized planet not be called a planet. If this comes to be true, I'm sure the IAU will change the definition of planet.
GreWi: Did I understand it also correct, that the strange orbits of Sedna, "2012 VP113" (and the orbits of possible others...) do point to the existence of an even bigger, major planetary body like a Super-Earth or even bigger?
Sheppard: Yes, the orbits of these very distant known objects seem to cluster together and one of the explanations is that it could be from a large massive object in the outer solar system shepherding these objects into these similar orbits.
GreWi: But such a large object would surely qualify as a planet?
Sheppard: One would think so, but the current IAU definition would not, so the IAU definition would have to be changed.
GreWi: Could this large object also be also a large gaseous planet, a "Dark Jupiter" or even a brown dwarf, like a stellar companion?
Sheppard: No, the object would not be as large as Jupiter since something that large would likely have been seen by now. But a rocky super Earth with a mass between 1 to 10 Earth masses could have gone undetected to date.

Dwarf planet "2012 VP113" through the telescope. | Copyright: Carnegie Institution for Science/ Scott S. Sheppard

GreWi: How strong do you judge the indications or even evidence for the existence of such a large body based on your new calculations?

Sheppard: We are using the two dwarf planets (Sedna and "2012 VP113") that are in the very distant solar system plus a few other objects that are closer to Neptune. Based on these few objects it suggests there might be a massive object out there, but it is only circumstantial evidence. There might be another explanation for the similarity of the orbits that we have not thought of. What we really need is to discover more of these very distant objects to confirm that they are bunch together with similar orbits.
GreWi: If one reads your press release you and your colleagues point very prominently to the "large-planet-theory". Is this your favorite theory – and if so, why is that?
Sheppard: We really don't know why these objects have similar orbits. A larger body in the outer solar system could create them. It is also possible that there is some observational selection effect that makes it easier to discover bodies with these kinds of orbits. We don't think there is any observational bias, but it is possible. The larger planet theory is just a theory that fits what we see, but it is not a sure thing.
GreWi: Given what you know now about the orbits of Sedna, "2012 VP13" and some Kuiper-belt objects, the lay-person (like me…) would think it should be possible to pinpoint the precise location of this massive "disturber" relatively easy. So why can't we find it?
Sheppard: This may sound plausible on a first thought as for example Neptune was actually predicted based on Uranus' uneven motion. But Uranus' orbit was known very well. We don't yet have the precision on the orbits of these distant objects to make such calculations.

Illustration of dwarf planet Sedna. | Copyright: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

GreWi: Because of the distance of the possible rocky-planet-sized bodies and in special of the distance of the possible large body to the sun, the classical ideas of the habitable zone exclude the possibility of life on these objects. However, in the last few years, several colleagues of you (like Abbot & Switzer) described several scenarios under which life could have been formed also outside the classical habitable zone and even on 'rogue planets' as long as another energy-source (instead of a star/sun) is available.

Do you see a way that the described objects - in case they exist - could be habitable or even already bear live (in whatever form)?

Sheppard: It would be unlikely, but a very massive object, bigger than Earth might have enough internal heat to allow some sort of liquid to exist under its surface. If this were the case, it is possible life could form, but unlikely.
GreWi: So fluids - like water - on such an object's surface are impossible?
Sheppard: The surface would be very cold. "2012 VP113" is likely minus 400 degrees Fahrenheit. So no chance for liquid on the surface of these objects because they would radiate their heat away to space very quickly and freeze any liquid on the surface.
GreWi: Could a possible atmosphere on these objects protect the heat from radiating into space?
Sheppard: Well, the only way an object would have an atmosphere to keep in the head would be if it were a gas giant planet. Any other atmosphere would just be frozen on the surface.
GreWi: Just last week other astronomers reported that the WISE mission could not find any evidence and traces of the long theorized and searched "Planet X". While their model still leaves a little space for the existence of such bodies, how can you explain the seemingly opposite conclusions based on the WISE-data to your latest finding?
Sheppard: WISE was only sensitive to objects Neptune sized or larger while the object we are suggesting would be smaller than Neptune.
GreWi: Mr. Sheppard, many thanks for your time and your interesting and informative answers.

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