- 4232 -
EXOPLANETS - and free floating
planets. Hundreds of Free-Floating
Planets Found in the Orion Nebula. It
appears that rogue planets, free floating worlds that aren’t gravitationally
bound to a parent star might be more common than we thought.
--------------------- 4232 - EXOPLANETS - and free floating planets
- The search for
extraterrestrial intelligence (SETI) will likely be sped up thanks to new
results that narrow down how alien radio signals would drift in frequency as a
result of the Doppler shift caused by their home planet's orbit around its
star.
-
- A Doppler shift is
the lengthening or shortening of the frequency of a signal caused by the motion
of the transmitter. If the transmitter is moving away from us, the wavelength
becomes stretched and the frequency decreases; if it's moving towards us, the
wavelength shortens and and the frequency increases. This results in the signal
appearing to "drift" across a range of frequencies as the transmitter
moves.
-
- Both the orbital
motion and the daily rotation of an exoplanet, plus Earth's own orbital motion
and daily rotation, contribute to the frequency drift of any signal that may be
transmitted from the exoplanet and received here on Earth.
-
- Radio astronomers
know that Earth's orbital motion causes a drift rate of 0.019 nanoHertz
(nHz is 10^-9 or 0.000,000,0001 cycles per second) and that
Earth's spinning on its axis creates an additional 0.1 nHz drift. These shifts
can be accounted for when analyzing signals.
-
- The drift rate is
also dependent upon the orbital characteristics of an exoplanet and the
inclination of its orbit with respect to us, how far from circular its orbit is
and how much it precesses, or wobbles.
-
- Machine-learning
algorithms that are able to sift through data, looking for signals that display
a drift rate, require a maximum value for the drift rate so that they can limit
their search. SETI searches usually assume a small value for the frequency
drift, less than 10 nHz, but previous calculations based on actual measurements
of the most extreme exoplanet orbits known placed an upper limit on the drift
rate of plus or minus 200 nHz.
-
- By modeling about
5,300 exoplanets, astronomers were able to refine and reduce the maximum value
for the drift rate caused by the orbital motion of exoplanets to plus or minus
53 nHz. This means that, for 99% of
planetary systems, the frequency of a signal detected from a distant exoplanet
would be expected to drift in frequency at a maximum rate of plus or minus 53
nHz.
-
- The current catalog
of known exoplanets is not entirely representative of the wider population of
exoplanets out there. Current detection methods still favor larger planets
closer to their stars, because they are the easiest to find. To avoid any biases, they also measured the
maximum drift rate of over 5,000 simulated planets that we might expect to be
more representative of the true population of exoplanets in terms of their orbital
characteristics, with smaller planet sizes, longer orbital periods and a more
uniform spread of orbital inclinations.
-
- The imagined
planets were placed into 20 groups, each consisting of 5,286 worlds, split into
10 groups with nearly circular orbits and 10 groups with increasingly
non-circular (known as eccentric) orbits. From these astronomers were able to
derive much lower drift rates, plus or minus 0.27 nHz for the low-eccentricity
orbits and plus or minus 0.44 nHz for the high-eccentricity orbits.
-
- As a wider range of
alien worlds are discovered in the future by upcoming missions such as the
European Space Agency's PLATO (Planetary Transits and Oscillations of stars),
the maximum drift rate calculated from real exoplanetary data should begin to
better reflect the values seen in the simulated results.
-
- Drift rates are one
way to tell whether a signal has come from deep space, although it is not a
foolproof method. Radio frequency interference (RFI) from transmitters on
Earth, cell phones, airport radars and so on,
have a drift rate of zero because they are on Earth with our receivers.
Satellites in low Earth orbit usually have negligible drift rates, but some,
such as SpaceX's Starlink mega-constellation and the U.S. government's GPS
network, do exhibit some frequency drift in their radio signals.
-
- New data from the
James Webb Space Telescope have revealed 540 planetary-mass objects in the
Orion Nebula and Trapezium Cluster.
This would be by far the largest sample of rogue planets ever
discovered. Last year, 2022, astronomers found 70 free floating worlds
throughout the Milky Way.
-
- The researchers
say a near-infrared survey from JWST allowed them to discover and characterize
this large sample of 540 planetary-mass candidates. The team says these
planetary mass objects (PMOs) are too small to be stars, as their masses are
well below the traditional cutoff for a deuterium-burning brown dwarf, even
down to 0.6 Jupiter mass, not much more massive than Saturn.
-
- Within the large
group of rogue planets are 42 pairs of planets that are gravitationally bound
together, something that’s never been observed before. The astronomers named
them Jupiter Mass Binary Objects, or JuMBOs.
-
- How pairs of young
planets can be ejected simultaneously and remain bound, weakly at relatively wide separations,
remains quite unclear. These
planetary-mass binary objects is a result that is highly unexpected and which
challenges current theories of both star and planet formation.
-
- The conventional
definition of a planet is that it is in orbit around a star. Current theories of planetary formation
suggest that Jupiter-sized objects can only be formed through the process that
gives rise to stars inside the clouds of dust and gas found in a nebula.
-
- It is clear that
further simulations and modeling will be needed to understand how a substantial
population of objects can form below 5 Jupiter masses and how a significant
fraction of them can end up in multiple systems.
-
- The exact
mechanisms for how planets go “rogue” are unknown, but several theories exist.
The theories include that planets are pulled away from one star by
gravitational interactions with other passing stars, or that supernovae kick
them out, or that they free float into space after their sun dies.
-
- Alternatively, for
the JuMBOs, the researchers speculate that planetary ejections can be caused
through planets scattering in a planetary disk or by dynamical interactions
between stars. The latter are
relatively common in dense star-forming regions like the Trapezium Cluster.
-
- Rogue planets are
usually impossible to image in visible light, which makes JWST’s sensitive
infrared vision the perfect tool to look for them. The Orion Nebula has been studied for decades
to observe the formation and early evolution of stars and other celestial
objects.
- The Orion
Nebula lies 1,350 light years away from
Earth and is visible to the naked eye as a misty smudge at the bottom of the
Orion constellation, part of the ‘sword’ of the mythical Greek hunter after
whom the constellation is named.
-
-
November 22, 2023
EXOPLANETS - Free floating planets 4232
------------------------------------------------------------------------------------------
-------- 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, November 22, 2023 ---------------------------------
No comments:
Post a Comment