75
votes
Accepted
Considering our methods of exploration, how likely is it that there are unfound planets (not dwarf planets) in our solar system?
There are no undiscovered planets between the sun and Neptune.
Objects closer (to Sun) than Neptune that are large enough to be considered planets (and not dwarf planets) can't remain 'hidden'. If it'...
- 4,137
69
votes
Why does it take so long to transmit an image from New Horizons to Earth?
New Horizons has just passed the Kuiper Belt Object (KBO) 2014 MU69 also known as Ultima Thule. KBOs form a belt of asteroids (the Kuiper Belt) from Neptune's orbit outwards and of which Pluto is the ...
- 8,312
60
votes
Is there enough matter orbiting the sun to make a second sun?
The vast majority of the stuff in the solar system other than the Sun itself is contained in one body, Jupiter. The total mass of the solar system is estimated to be about 1.0014 solar masses, or ...
- 33.5k
58
votes
Accepted
Why hasn't the "9th Planet" been detected already?
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 ...
- 1,291
58
votes
How can comets have tails if there's no air resistance in space?
There are two forces that can cause the formation of a tail: the solar wind and radiation pressure.
The first misconception in your question is "the dust [travels] slower than the nucleus". The tail ...
- 116k
52
votes
Accepted
Why won't the Sun set for days at N66.2 which is below the arctic circle?
From the PyEphem Quick Reference Guide:
Rising and setting are sensitive to atmospheric refraction at the
horizon, and therefore to the observer’s temp and pressure; set the
pressure to zero to turn ...
- 4,695
48
votes
Accepted
What makes protoplanetary disks start rotating? (Initial energy needed to rotate)
Two rocks placed in space with no relative motion are going to be attracted by gravity, and hit. 3 rocks, placed in space with no carefully rigged symmetry, will likely miss each other, as the ...
- 4,470
47
votes
Why does it take so long to transmit an image from New Horizons to Earth?
The other answer mentions it, but this gives a bit more theory as to the why.
It's effectively for the same reason that your phone or Wi-Fi don't work as well and slow down when that they are far ...
- 1,106
46
votes
Why is the Sun's density less than the inner planets?
The sun isn't the same density all the way through.
According to MSFC's solar interior page, the core density at the centre of the sun is a whopping 150,000 kg/m$^3$. Surrounding it the radiative ...
- 2,467
45
votes
Accepted
Why do the planets orbit in the same direction?
The same reason (almost) all of them rotate in the same direction: because of the conservation of angular momentum.
Before a star and its planets exist, there’s just a cloud of disorganized gas and ...
- 8,119
43
votes
Is it odd that our Sun has so many planets?
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 ...
- 3,103
43
votes
Accepted
Closest star system to Alpha Centauri?
The sun is the nearest star to Alpha Centauri (unless you count Proxima Centauri, which is really part of the same system).
There is a very small and dim pair of brown dwarfs, called Luhman 16 that ...
- 116k
42
votes
Why do things float in space, though the gravity of our star is always present?
It is not true that "objects float around" in the solar system.
Perhaps you have seen video from the space station, and you can see things floating. This is not because there is no gravity, but ...
- 116k
41
votes
Accepted
Which planet, viewed from which other planet would appear the largest?
Here is a table with planets, their minimum/maximum distances from the Sun, their minimum distance (assuming the planet's aphelion and its neighbour's perihelion coincide, which they don't, so the ...
- 4,780
40
votes
Is Jupiter a failed star?
No.
Besides the 13 Jupiter-masses required to ignite deuterium burning, and make Jupiter into a Brown Dwarf, there is a clear difference between the formation pathways of Brown Dwarves and Gas ...
- 9,757
39
votes
Can a planet in our system eclipse the sun as seen from another one?
In our solar system, it is possible for one planet to partially eclipse the sun, but it is not possible for any planet to cause a full solar eclipse as seen from another planet.
The sun is too big and ...
- 16.2k
38
votes
Why hasn't the "9th Planet" been detected already?
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 ...
- 3,010
38
votes
Could we detect the light of cities at night in other solar systems?
No. There are very few exoplanets that can even be imaged as "dots". There are none that can be resolved as discs and it would be well beyond current technology to see lights on the ...
- 116k
36
votes
Accepted
9th planet location?
It's too dim to be seen during a normal survey during the majority of its
orbit.
Update: Scientists at the University of Bern have modeled a hypothetical 10 Earth mass planet in the proposed orbit to ...
36
votes
How can comets have tails if there's no air resistance in space?
First, there is not just one tail, it is several, but when traveling far from a star, they are "aligned". When it gets closer the different materials behave differently, both depending on the ...
- 461
36
votes
Accepted
Which planet came first in our Solar system?
The planets (probably) formed by the accumulation of planetesimals, and they all formed over roughly the same time span. Inner protoplanets had access to more matter, so they probably were able to ...
- 13.3k
34
votes
Accepted
Why do planets and satellites in the Solar system look so wildly different if they came from more or less the same matter?
This questions can be split in two; for planets and satellites.
The diversity of planets reflects in part the diversity in terms of chemical composition of the protoplanetary disk. We know that UV ...
- 3,856
34
votes
Accepted
How can Io be tidally heated while it is in tidal lock?
How can Io be tidally heated while it is in tidal lock?
It is tidally locked in a mean motion sense of "tidally locked". That Io is in an eccentric orbit rather than a circular orbit means ...
- 33.5k
34
votes
Accepted
Where was the solar system born? Alternatively, how far back in time can we retrodict the location of the solar system?
Basically no, and not very far back at all.
Star forming regions generally last for at most 10 million years. The "nebula" in which the Sun was born is long gone so cannot be identified.
The ...
- 146k
33
votes
Why do things float in space, though the gravity of our star is always present?
To help with James K's excellent answer, a visual representation might help. Let's look at a thought experiment - Newton's Cannonball.
Let's say you have a cannon, high enough that it's being held ...
- 421
33
votes
Could we detect the light of cities at night in other solar systems?
I did a few rough calculations.
Let's assume a neighbor system (4 light years), and a population of 1 billion people each transmitting 1000W of light into the night sky.
Then on Earth, a 100 square ...
- 1,449
31
votes
Is it at all possible for the sun to revolve around as many barycenters as we have planets in our solar system?
The short answer is no; there is only one barycenter. Yes, you can count the Sun/Jupiter barycenter or the Sun/Saturn barycenter, or whichever barycenter you want, but the net effect of all Solar ...
- 6,721
30
votes
Why is the Sun's density less than the inner planets?
Fusion inside of a star affects the sun's density (which does not happen with a planet). It produces an outward pressure that balances against the attraction of gravity, thereby reducing the density ...
- 6,254
30
votes
Accepted
How is it possible for a collision to be responsible for Uranus's axial tilt?
For objects on the scale of a planet, the state of matter doesn't really matter much. A colliding planet or planetesimal would not "just pass through" The amount and density of the gas ...
- 116k
29
votes
Accepted
Starting a fire in a cold planet that was full of flammable gas
The outer parts of Neptune are mostly hydrogen and helium. There are small amounts of other gases such as methane, ammonia and water vapour. However, there is no oxygen at all.
If you took some of ...
- 116k
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