- 4303 - EARTH'S and PLANET'S MAGNETIC FIELDS? - Observations of a faraway rocky world that might have its own magnetic field could help astronomers understand the seemingly haphazard magnetic fields swaddling our solar system’s planets. And maybe our own magnetic field
---------------
4303 - EARTH'S and PLANET'S
MAGNETIC FIELDS?
- The Milky Way is full of alien worlds that might make their own magnetic fields. Astronomers just need to find them.
-
- For decades,
astronomers have been perplexed by planetary magnetic fields. In our own solar
system, there is no rule that explains which worlds generate these magnetic
sheaths: Earth has one, but its sister world,Venus, does not.
-
- Astronomers
suspect that one of the best ways to understand the mysteries of magnetism
might be to study worlds orbiting other suns. By collecting a census of
exoplanet magnetic fields, researchers could determine whether they are common
features of other worlds.
-
- Why does one rocky
planet have a magnetic field while the other does not? It has been a challenge to build such a
census and to even find exoplanet magnetic fields because these fields are
faint and hard to detect.
-
- But in April, two
independent teams found what appears to be the signature of a magnetic field
produced by a rocky planet orbiting a small, dim red dwarf star about 12
light-years away. The planet, “YZ Ceti b”, is slightly smaller than Earth and
likely too hot for life as we know it.
-
- We know from our
solar system that magnetic fields play an important role in affecting how a
planet loses or retains its atmosphere over time. In our solar system, Earth and the four giant
planets, Jupiter, Saturn, Uranus and Neptune, have significant magnetic fields.
Mercury has only a faint field, and Mars very likely had a more robust field in
the past, which it lost for reasons that aren’t understood.
-
- Planetary magnetic
fields are generated by an engine called a “dynamo”, which is built from molten
metal churning in a planet’s core. That churning produces electrical currents
that drive a magnetic field. On Earth and the four gas giants, this process is
strong enough to form a protective cocoon around the planet, deflecting charged
particles that would otherwise blow away the planets’ atmospheres.
-
- Scientists suspect
that many of the 5,000 known exoplanets have magnetic fields, but detecting
them is a different matter. In the 1970s, astronomers surmised that when a
planetary magnetic field interacts with the planet’s host star, it might
produce an observable spike in low-frequency radio waves emitted by the star,
known as “auroral emissions”.
-
- The timing of
those spikes, as seen from Earth, would depend on a planet’s location in its
orbit. The atmospheric data was taken from four hot
Jupiters, giant planets orbiting close to their stars, to get a hint of
magnetic fields in 2019. In 2021 they detected a radio signal linked to a
planetary magnetic field in the Tau Boötes system, 51 light-years from Earth.
-
- In 2021
astronomers detected ultraviolet emissions from a Neptune-like planet, “HAT-P-11 b”, 123 light-years from Earth,
that suggest the planet’s magnetosphere.
But none of the detections were definitive and none were of rocky planets.
-
- In 2017,
astronomers found exactly the system they needed for the type of indirect
observation they’d hypothesized about for nearly 50 years. Three rocky planets
orbited the red dwarf “YZ Ceti”, a
cosmic stone’s throw away. The system’s proximity to our own makes its planets
convenient targets, especially YZ Ceti b, the innermost planet.
-
- Red dwarfs
typically have stronger magnetic fields than stars like our sun, which makes it
easier to identify the fingerprint of an orbiting planet’s magnetic field. The planet would need a magnetic field
strength similar to Earth’s to cause the brightness of radio waves.
-
- A more definitive
detection would require more observations of the star and the periodic radio
spikes. Astronomers are hoping that
similar observations can be attempted for the TRAPPIST-1 system of seven
Earth-size worlds orbiting a red dwarf 40 light-years from Earth, or even for
the red dwarf Proxima Centauri, the closest star to Earth at 4.25 light-years,
which hosts a rocky planet.
-
- Finding
exoplanetary magnetic fields is crucial for understanding how prevalent they
are and how planets make magnetism. In
our solar system, a dynamo seems to be key. But a dynamo might not be the only
way to generate a planetary magnetic field, especially in “super-Earths”,
worlds that are between Earth and Neptune in mass, which are among the most
common type of exoplanet spotted so far.
-
- Would heat
fluctuations within a planet do the job inside worlds that have molten
interiors but lack a solid core. Would
a magma ocean produce a magnetic field? Magma oceans should be pretty common in
super-Earths.
-
- “GO-LoW” program would use a fleet of thousands of
small spacecraft to study radio waves from exoplanets. Another idea is
“FARSIDE”, a proposed radio array from NASA that would be placed on the far
side of the moon, free of radio interference from Earth.
-
- Astronomers using
the James Webb Space Telescope have spotted what may be the smallest known
brown dwarf, a "failed star" that's only three or four times larger
than Jupiter.
-
- The tiny
proto-star in a star cluster “IC 348”,
is located 1,000 light-years from Earth. The object is likely to be a brown
dwarf, a type of celestial object that blurs the line between planet and star.
-
- Brown dwarfs are
not quite stars, but they come close. Essentially, they are stars that failed
to ignite, earning them the unflattering nickname "failed stars."
Brown dwarfs are not massive enough to sustain typical hydrogen fusion in their
cores. However, they do have enough mass to emit light and heat from fusing a
specialized type of hydrogen, called deuterium. Deuterium is a stable form of
hydrogen with an added neutron, whereas normal hydrogen only has a proton in
its nucleus.
-
- Most stars are
incredibly dense compared to even the biggest planets; our own sun is about
1,000 times the mass of Jupiter, the largest planet in our solar system, but
its diameter is only 10 times that of Jupiter.
-
- In comparison, a
large brown dwarf could pack about 80 Jupiters inside. But this particular
brown dwarf is only three or four times more massive than Jupiter. This easily makes it the smallest
"star," or star-like object, ever discovered. It is also very young;
the star cluster that it belongs to is just 5 million years old.
-
- In addition to
being minuscule, the brown dwarf and its neighbors appear to have an intriguing
molecule floating around in their atmospheres. The researchers detected a
spectral signature from an unidentified hydrocarbon, a molecule that contains
some of the raw ingredients for life as we know it.
-
- NASA's Cassini
probe detected the same molecular signature in the atmosphere of Saturn's moon
Titan, but this is the first time it has been seen outside of the solar system.
-
- The
record-breaking find of a star 43,000 times more magnetic than the sun could
help unravel the mystery of how magnetars form.
The star, “HD 45166”, has a unique, helium-rich spectral signature that
hints at an unusual origin.
-
- Neutron stars are
the densest known celestial objects in the universe, packing a sun's worth of
mass into a ball no wider than a city. Their highly magnetic versions,
magnetars, have some of the strongest known magnetic fields in the universe.
Neutron stars and magnetars form in the wake of massive supernova explosions,
when the leftover material from a dead star condenses back into an extremely
dense, hot object.
-
- But astronomers
are still trying to understand what conditions produce magnetars versus regular
neutron stars. Located 3,000
light-years from Earth in the constellation Monoceros (the Unicorn), “HD 45166”
has puzzled scientists for more than a century.
-
- The star behaves
similarly to a type of extremely bright stellar object known as a “Wolf-Rayet
star”, except that it is smaller, dimmer and has an abnormally high
concentration of helium. However, nobody had put forth a satisfactory
hypothesis to account for its weird spectral signature, until now.
-
- Using data from
several ground observatories, astronomers discovered that HD 45166 is extremely
magnetic, a record-smashing 43,000 times more magnetic than the sun. The
researchers suspect that, unlike most massive helium stars, which evolve from
red supergiants, HD 45166 formed during a merger between two smaller stars.
They also believe that in several million years, it will explode into a modest
supernova and re-form as a magnetar.
-
-
This raises the question of how many magnetars come from similar systems and
how many come from other types of systems. In the meantime, this proto-magnetar
represents a new type of stellar object never seen before, a massive magnetic
helium star
-
-
January 1, 2023 EARTH'S
and PLANET'S MAGNETIC FIELDS? 4303
------------------------------------------------------------------------------------------
-------- Comments
appreciated and Pass it on to whomever is interested. ---
--- Some reviews are
at: -------------- http://jdetrick.blogspot.com -----
-- email feedback,
corrections, request for copies or Index of all reviews
--- to: ------
jamesdetrick@comcast.net
------ “Jim Detrick” -----------
--------------------- ---
Wednesday, January 3, 2024 ---------------------------------
No comments:
Post a Comment