41
votes
Accepted
Can a tectonically inactive planet retain a long-term atmosphere?
Yes, a tectonically inactive planet can retain a long-term atmosphere.
You make the connection that a lack of plate tectonics on a planet indicates a "dead" core and thus said planet has no ...
- 15.1k
37
votes
Can a magnetic field of an object be stronger than its gravity?
It depends on what object it's acting on. There are many objects, including stars, that have magnetic fields where Lorentz forces on charged particles like electrons and protons are stronger than the ...
- 5,336
33
votes
Are stars attracted to one another by their magnetic fields?
They behave just as other magnetic fields do - whether the force is attractive or repulsive would depend on the relative orientation of the fields. But magnetic forces are negligible compared with ...
- 158k
27
votes
Why do sunspot rise in number "precisely" every eleven years?
Why is the periodicity so steady?
It's not so steady. Some solar cycles have lasted for nine years, others for fourteen years. Of the 26 solar cycles between 1700 and the present, 21 had a span ...
- 34.4k
19
votes
Accepted
How could Mars' atmosphere be shed by solar winds, when Venus has a thick atmosphere despite no magnetic field?
I am not certain that the main cause of Mars losing most of its atmosphere was the solar winds.
Long before the solar wind was discovered scientists calculated other factors which affect how long a ...
- 7,884
18
votes
Accepted
Has a magnetic field flip of a distant star ever been measured?
The Sun's magnetic activity cycle of $\sim 22$ years involves a large-scale reversal of the polarity of the magnetic field every $\sim 11$ years.
There are very many observations of other solar-type ...
- 158k
17
votes
Accepted
Can a magnetic field of an object be stronger than its gravity?
Let's look at the proper magnetic force (as opposed to the Lorentz force on a moving, charged object described in @KenG's answer) on a specimen $S$ of magnetized material with mass $M_S$ as a way to ...
- 30.2k
16
votes
How big is the energy content of the magnetic field of the Milky Way?
Yes, the energy of the Galactic magnetic field is substantially smaller than the mass-energy of the Milky Way. The total energy of a magnetic field $\mathbf{B}$ in a volume $\mathcal{V}$ is
$$E=\frac{...
- 37.3k
15
votes
Accepted
Could two celestial bodies with extreme magnetic fields affect each other's motion via magnetism?
The gravitational force declines as $1/r^2$ while magnetic field from a dipole goes as $1/r^3$: hence magnetic forces typically become negligible over longer distance, unless the source is extremely ...
- 15.1k
14
votes
How could Mars' atmosphere be shed by solar winds, when Venus has a thick atmosphere despite no magnetic field?
One of the main loss mechanisms of atmospheres escape is thermal escape (Jeans escape) into space. The average thermal velocity at a given temperature $T$ for a molecule of mass $m$ is
$$ v_{th} = \...
- 20.4k
13
votes
Accepted
Are there neutron stars whose magnetic axis and rotating axis are the same, and if so what will happen?
It is believed that old pulsars may have their rotational axes closely aligned with their magnetic field. This would happen over a timescale of $\tau\sim10^7$ years (Lyne & Manchester (1988)). ...
- 37.3k
10
votes
Why are the magnetic poles of a pulsar so far off the rotational axis, yet stable?
The polar offset is not stable. Most researchers now think that the angle between the rotation axis and the magnetic field axis decreases with time. This is thanks to the same torquing mechanism which ...
- 158k
9
votes
Can a magnetic field of an object be stronger than its gravity?
It isn't impossible, but the short answer is "no".
A gravitational field will accelerate all matter and energy equally while a magnetic field will only accelerate moving electric charges (other ...
- 91
9
votes
Accepted
Earth's magnetic field vs. refrigerator magnet
Can any magnet (or even one much stronger) of the Earth divert the cosmic rays as Earth's?
No, because even if the strength of the field may be higher, the size of magnetic field is too small. ...
- 2,233
8
votes
Why has Venus's atmosphere not been stripped away by solar wind?
A major factor, is that Venus' volcanoes are still active. Mars's died millions of years ago. If they were still erupting, then Mars' atmosphere would be much thicker today.
Edit: This may actually be ...
- 99
8
votes
Accepted
Is it possible to tell if a certain extrasolar planet produces its own magnetic field?
There are three approaches with which people have looked for this, and not yet been too successful:
A transiting planet planet with a strong magnetic dipole and/or very strong host star winds might ...
- 9,849
8
votes
Accepted
What forces expelled these huge clouds, then blocked further progress, yet allowed it to maintain its threads?
This was a coronal mass ejection.
Those 1973 astronomers weren't looking at the picture correctly. They didn't have the tools at that time to look at the picture correctly. Coronal mass ejections (...
- 34.4k
8
votes
Accepted
Why does the solar wind switch to flowing straight by the time it reaches Earth?
When plasma moves in a magnetic field then the charged particles follow helical paths around the field lines, due to the $q\vec{v}\times \vec{B}$ Lorentz force. If the radius of gyration is small, ...
- 158k
8
votes
Why is the Earth's magnetic field stronger than its neighbors?
I've learned that the Earth's core is hot due to decay of radioactive elements.
This is unproven, non-standard geophysics. There are several arguments against this. One is that all of the long-lived ...
- 34.4k
8
votes
How big is the galactic magnetic field in the solar system and how can we measure it?
There is no galactic magnetic field inside the (inner) solar system. The solar wind is a near-perfect plasma and according to the frozen-in theorem it carries the magnetic field of the Sun with it ...
- 20.4k
7
votes
Accepted
What causes Titan a moon to have a denser atmosphere than that of a Mars?
Mars and Titan differ markedly in distance from the Sun, composition, and possibly geological activity.
Titan is about 6.3 times as remote from the Sun as is Mars, which means Titan receives about 1/...
- 34.4k
7
votes
Accepted
Roche Zone of a black hole vs Roche Zone of Neutron Star
The Roche limit is defined in classical physics, dealing with materials that behave classically. That said, of course people have tried to estimate the counterpart in relativistic conditions. It turns ...
- 15.1k
6
votes
Magnetars and the Dynamo Effect
There are, in general, two classes of explanations for neutron star magnetic fields: fossilized magnetic fields and active magnetic fields (see here for an early overview on some of the internal ...
- 37.3k
6
votes
Magnetars and the Dynamo Effect
Magnetars (and neutron stars in general) don't need a dynamo to create their magnetic fields. Their magnetic fields are "frozen in" at the time of their formation. To really see why this is, you have ...
- 15.1k
6
votes
Reversal of magnetic poles of earth
The Earth will keep revolving in the same direction during a geomagnetic reversal.
There have been a few articles about this phenomenon published during 2018:
National Geographic - No, We're ...
- 1,420
6
votes
Accepted
Does the sun have cycles causing temperature changes on Earth?
The Sun's magnetic field is way too weak to have any measurable effect on the Earth's orbit. The sunspot cycle does produce a small but detectable signature in the global average temperature (about $0....
6
votes
Are there areas within Jupiter's magnetosphere without powerful radiation?
I'm sure that some of the other answers will have data about the shapes and dimensions of radiation belts around Jupiter and the other giant planets in the solar system.
Possibly you should study the ...
- 7,884
6
votes
Does the coriolis force help shape the magnetic field of the sun?
Yes. For example in "The Sun and its Restless Magnetic Field"
(Manfred Schüssler)
The forces which are most
important for the dynamics of a magnetic flux tube are the buoyancy force,
the ...
- 127k
6
votes
Accepted
Seasonal variation of aurora and magnetic activity
I had to look this one up. It is a genuine effect, not just an observational bias. The frequency of aurorae has been recorded with automatic cameras on timescales of a decade, showing that the ...
- 158k
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