# Tag Info

1

Venus, I propose, because it (almost) doesn't rotate. The winning (aristotelian) argument for geocentrism before Galileo was the idea that everybody's' hats would fly off by the (ethereal) air drag if the Earth rotated any faster than a horse in gallop (let alone at Earth's crazy 465 m/s compared to Venus' 1.8 m/s). Long nights too, as previously said. And ...

1

I think Mercury has some of the points that Mars has. Plus: - a highly eccentric orbit, making it more obvious that planets have ellptical orbits, - no moon, which is great to avoid falling into the pitfall of thinking about being at the center of the universe, - a very long solar day (about 6 earth months or two mercurian years), leaving plenty of time to ...

1

I will argue Mars. A smaller diameter makes it easier to determine the round shape of the planet, and determine the diameter more exactly. A thinner atmosphere and almost no clouds are better conditions for sky observation. The small orbital radius of the Mars moons makes it easy to figure out the distance to them. (For example, Phobos is only in the sky ...

0

(DISCLAIMER) I am not an expert on this subject, and I only hope that my answer will attract better, and more complete ones. The Meeus book that @Gerard Ashton mentioned is a great resource for amateurs, but I am worried whether it is accurate enough for, let's say, eclipse or transit predictions. Also I glanced at the site linked in the question and saw ...

3

This question already has muliple answers on this site... However : Yes, astronomers DO have enough data to speculate about a possible Ninth Planet. The orbits of six KBO are correlated, and a possible ninth planet could be the reason for those peculiar orbits. See image below for the computed results of the possible orbit of the ninth planet.: ...

3

Other than being kind of in the "Goldilocks" range, meaning, not too big, not too small, (not to be confused with Goldilocks-zone, that's something else), there's nothing special about our sun. There might be something a little unusual about Jupiter's movement over the last 4 billion years and perhaps, something unusual in the just right formation of our ...

0

In terms of absolute size, the sun is at the smaller end of the spectrum (the largest stars can be over 100x the mass of the Sun) but due to the skewed mass distribution in stars, the number of these massive stars is very low and the sun actually lies in the top 5% of stars by mass. The size of the sun is definitely not unique, nor are any of its properties ...

3

One thing that is, if not unique, unusual about the Sun is the size of it. It belongs to the top 5% brightest stars, meaning that 19 out of 20 stars are smaller than the Sun. Having a Jupiter size planet is certainly not unique, and plate tectonics we know nothing about for exoplanets.

0

You've probably long since moved on, but, just for reference, the initial conditions HORIZONS uses are mentioned ("header.431_572") in ftp://ssd.jpl.nasa.gov/pub/eph/planets/Linux/README.txt but the only place I could find them in "table form" is in my own git repository: https://github.com/barrycarter/bcapps/blob/master/ASTRO/header.431_572 The ...

4

There may be Sednoids there. Sednoids are a hypothetical class of "inner Oort Cloud objects" named after their prototype, Sedna. Sedna's aphelion is ~936 AU, bringing it close to the inner boundary of the Oort Cloud. Sednoids may have aphelions ranging from about 100 AU to 1,000 AU. The problem is, only two Sednoids have beet detected to date, 90377 Sedna ...

2

You would not actually be able to see that much, the sunlight is less than 4% of the strength at Earth's distance to the Sun. That is still enough to see though (Much brighter than Moon light at night in fact). The problem is the transparency of the atmosphere; we can not look in, you can not look out. You would only see a weak brown or red glow below the ...

1

The Kuiper belt and the Scattered disk are widely believed to lie in the space between the outer planets and the Oort cloud, but not to reach all the way out to the Oort cloud (apparently due to resonances with Neptune and a scarcity of sighted object much outside the 1:2 resonance orbit). The various dwarf planets of the outer solar system are sometimes ...

1

[Not sure if I should answer this, but I will try to answer something while trying hard to not go off-topic.] The planets aspects Mercury surface is essentially a collection of small random craters with no discernible pattern at all, so you might not consider which side is presented. The only distinguished feature is a set of dark craters in its north ...

6

Inner. The entire asteroid belt is in the Inner Solar System (now). The definition of "Inner" vs. "Outer" is non-arbitrary, based on the current "frost line", approx. 5 a.u. radius. https://en.wikipedia.org/wiki/Frost_line_%28astrophysics%29 https://en.wikipedia.org/wiki/Solar_System#Inner_Solar_System

7

Ceres is 2.76 AU away from the sun, so the sunlight is seven times weaker. That is comparable to the levels of illumination 30 minutes before sunset on Earth, so you are not going to have any problem seeing the surface. The albedo of Ceres is quite low, comparable to worn asphalt. But it is still easy to see it.

1

I am not very familiar with orbital dynamics (so please correct me if I'm wrong). I was told that, for instance in the case of the mean motion resonances that cause the majority of the Kirkwood gaps in the asteroid belt, not only the ratio of the periods, but also the timing is important. Let's take Pluto as an example, which is in 2:3 resonance with ...

7

The inverse-fourth-power law you're referring to is valid for light emitted from a source, reflected non-specularly — i.e. in all directions — from a reflector, and detected by the original emitter. If the reflector is a mirror, the observed flux just follows the normal inverse-square law with the nominator equal to $(2d)^2$ instead of $d^2$, since the ...

2

The idea is basically to look for comets coming from the same direction. Look for a pair of comets that at some time earlier in their orbit was at the same place at the same time. That is a data point, but an extremely inaccurate one. It does not have to mean anything, and you are going to collect a large amount of statistical noise. For this purpose, normal ...

2

It is likely that during the formation of most stars, comets are formed from the same gas and dust that the star and any planets it hosts were formed from. Extrapolating what we know and strongly believe about our own star, the Sun, it is likely that many or most stars have a cloud of comets around them analogous to our Oort-cloud (which hasn't been ...

2

What they have at present is best described as a theory based on data that is not precise enough to make a definitive statement. They are telling people they think something is out there and roughly what they think it might be, but they really don't have accurate enough data to make any statements beyond that. The fact that the possible range of distances ...

3

Page 12 of Batygin & Brown (2016) says that a speculative formation scenario can be drawn from recent solar system formation simulations by Bromley & Kenyon and by Izidoro et al. These suggest that the core of a nascent ice giant may have been ejected very early in the solar system's history in order to explain the properties of the observed planets; ...

5

The recent possible discovery of Planet Nine by Batygin & Brown (2016) has caused quite a stir, in the astronomy community, Astronomy Stack Exchange, and the rest of the world. This is, of course, in part because any mention of such a discovery will cause a stir, but it is also in part because of the claimed probability if the movements of the ...

7

Thommes et al. (2001) ran simulations and found that, at optimal conditions (namely, a planet of ~ 10 Earth masses), migration can be complete with ~ 100,000 years. Note that this was done before in-depth research was done on the Nice model, which is very similar. However, the mechanisms are different, as are the planet masses. The difference in timescales ...

2

Batygin and Brown made a website which describes the search for the 9th planet in clear terms. They specifically note the following: perihelion (its closest approach to the sun) at around a Right Ascension in the sky of 16 hours, which means that the perihelion position is straight overhead in late May. Conversely, the orbit comes to aphelion (the ...

25

Brown and Batygin, the authors of the paper on the possible planet, have a webpage addressing this. A few reasons not already covered: It moves quite slowly - the authors estimate 0.2-0.6 arc seconds per hour - so standard surveys may not notice the movement and fail to recognize it as a solar system object. Eris, which is the most distant confirmed ...

5

The clipping above from the Albuquerque Journal doesn't really answer your question, but astronomers have been hunting for a largeish planet beyond Pluto for quite some time now. See also: http://www.zetatalk.com/theword/tword26b.htm http://www.bibliotecapleyades.net/hercolobus/esp_hercolobus_2_02.htm (under "United States Naval Observatory ...

7

Possible reasons that the planet has not been picked up previously: It's not there. Photographic proper motion surveys cover the whoke sky. To avoid these planet 9 would have to be fainter than about 18th or 19th magnitude. This puts a lower bound in the size/albedo/distance combination for any planet 9. The proposed planet could easily be fainter than ...

16

There are many normal methods that we use to detect exoplanets, but none of them work well in the case of the 9th planet. Here are some of the main ones. Radial velocity. The Sun is not moving significantly with respect to Earth, and the hypothetical planet is too far away from the Sun to have much of an impact. Transit. This is obviously impossible, as ...

18

This graph from XKCD says a lot about why that is the case The bottom line is, the 9th planet is too small to be detected through WISE, and too far/small to have been detected through visible observation. Most likely this hypothetical planet is a long ways away, possibly as far as 1200 AU, and not particularly large, making it difficult to see. WISE was ...

2

The introduction of the paper mentions some alternative interpretations put forward in earlier papers. It seems as if this "problem" has been noted earlier. This new solution to the problem beats earlier solutions. But maybe it is an evolving discovery process which again will invent new better explanations? In addition to those mentioned in the paper, I ...

6

There are two basic ways to detect such an object. First is to detect it through reflected sunlight. Second is from the heat that it produces. We already know that the reflected light of such an object likely would be around a 16.5 magnitude. To determine the infrared, we have to estimate the temperature The temperature very much depends on the composition. ...

4

Direct reflection of sunlight is the most likely scenario for a ninth planet discovery, however that does not hold if the object has a very low albedo. I assume you are interested in what wavelengths the planet would radiate. For the surface temperature, the rotation of the planet is important. If it is locked with one side facing the sun, or rotates very ...

8

The possible planet 9 is thought to be about 10 Earth masses and is unlikely to be a gas giant (it may be the core of an "interrupted" gas giant). As such, it will not be generating significant luminosity itself and would be rocky, or more likely, icy in character. It would thus only be seen by reflected light. The considerations for what wavelength to ...

5

Given that Kepler has detected stars with 5 or 6 planets that exist in an extremely flattened plane and much flatter than the solar system, then we can be reasonably sure that stars with more than 4 planets are reasonably common. Given the many mechanisms for scrambling the orbital inclinations out of a perfectly flat configuration, and that seeing multiple ...

12

What else could it be? Very simply, it could all be a coincidence... What they have done is noted that objects in the outer solar system have their orbits grouped in interesting ways. Someone suggested this might indicate there was a heavy planet (or core of a giant protoplanet) that influenced their orbits in this way; the recent announcement is the ...

15

From an exoplanet-finding point of view, the Sun has between one and three planets. The major exoplanet-finding techniques in current use involve watching for either periodic Doppler shifts as the planet's gravitational pull causes the star to wobble, or periodic brightness shifts as the planet transits the star. Both require that the planet is large ...

5

We can't detect whether there are or are not objects of similar "small" sizes orbiting other stars. We simply lack that level of ability. From a scientific point of view I'd simply say "don't know". From a practical point of view I would expect other stars to have systems with a huge variety of things in orbit - there's no reason not to expect this, but ...

-3

If you had access to a sufficient telescope, you could theoretically see it, if you looked in the right place (although no one knows where the right place might be). But if it's anywhere near aphelion there are only a handful of sufficient telescopes in the world (let's say an 8m mirror or larger), so I think it highly unlikely that you have access to one of ...

8

The parallax is found from a triangle with the Earth's orbit at its base. The annual parallax here would then be between 1/200 and 1/1000 radians ($\sim$ 1000 to 200 arcseconds) which is indeed enormous and much bigger than the likely proper motion during a year.

3

Maybe the Gaia space telescope has already caught it? First data release in mid-2016.

29

It's too dim to be seen during a normal survey during the majority of its orbit. The paper gives potential orbital parameters of $400-1500~\textrm{AU}$ for the semi major axis, and $200-300~\textrm{AU}$ for perihelion. Since the paper doesn't give a most-likely case for orbital parameters, I'm going to go with the extreme case that makes it most difficult ...

7

The position of the hypothetical object is not known with any certainty, so it's hard to know where to point your telescope. The paper proposes a wide range of orbital distances anywhere from 400 to 1500 AU semi-major axis, with a perihelion (closest approach to the sun) of 200-300AU. This is 8 times as far as Neptune. (I didn't read the article closely ...

5

Citing the original article: We find that the observed orbital alignment can be maintained by a distant eccentric planet with mass $\geq \approx 10$ m⊕ whose orbit lies in approximately the same plane as those of the distant KBOs, but whose perihelion is 180° away from the perihelia of the minor bodies. and As already alluded to above, the precise ...

8

Those are model calculations, which hint to the existence of a possible body of about 10-times the mass of Earth. Calling this a discovery would clearly be premature. The confidence level is just a little above the "evidence" level of 3 sigma, under the assumption, that the discoveries of the KBO objects leading to the inference aren't observationally ...

7

According to Caltech there is possibly a planet 10 times the mass of earth in a 15-20 thousand year orbit at an odd angle. It hasn't been observed yet. There's a search for it ongoing.

1

The prime candidate for the origin of interstellar comets, if any of those are around, are star systems which formed together with the Sun out of the same nebula collapsing into an open star cluster. Being captured from a Solar sibling might mean nothing more exotic than that. Same time of formation, same mixture of elements, same trajectory. That is more ...

3

The primary source of comets for our solar system comes from the Oort Cloud, a smaller amount coming from the Kuiper belt. The Oort cloud is thought to have originated from the remnants of a proto-planetary disk. This paragraph explains this better: The Oort cloud is thought to be a remnant of the original protoplanetary disc that formed around the Sun ...

3

What is the future of our universe? Like StephenG said, nobody knows for sure. But we do have confidence that the universe is expanding, and we also have confidence that the expansion is speeding up. So extrapolating from that, the future looks cold and lonely and bleak. A bit like life for the older generation! Is the universe heading towards a ...

1

Your guess is as good as any cosmologist's. We don't know how it came into being, not with any confidence. There are theories, but nothing definitive has emerged to explain where it all came from. This may be hotly disputed by proponents of each theory, but we're not there yet, IMO. We're not sure yet about what all the relevant forces are ( e.g. dark ...

Top 50 recent answers are included