From Newsgroup: alt.fan.heinlein
In the next week or two I hope to visit with my oldest grandchild, age
13, who lives out of state. She has started reading sci-fi, and I will
give her a copy of Arthur C. Clarkes "Rendezvous with Rama."
from
https://www.iflscience.com/we-may-have-our-third-interstellar-visitor-and-its-nothing-like-the-previous-two-79837
We May Have Our Third Interstellar Visitor And ItrCOs Nothing Like The Previous Two
If A11pl3Z is what we think, then the first three visitors werCOve found
are all very different.
Stephen Luntz headshot
Stephen Luntz
Freelance Writer
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Estimates of A11pl3Z's orbit are changing fast, but it is clear that it
barely bends on its way past the Sun, being very much a visitor from
outside the Solar System.
Image Credit: Catalina Sky Survey
Astronomers have detected an object with an orbit that will take it out
of the Solar System, and almost certainly must have come from outside as
well. Having recognized it long before it reaches its closest approach
to the Sun, we will have months to study it as it brightens. What we
already know, however, is that it has a much more extreme orbit than the
two previous examples, 'Oumuamua and Borisov, which in turn were quite
unlike each other in composition. Outside the Solar System, the universe
is a very diverse place.
In 2017, astronomers found something they had never seen before: an
object passing through the Solar System with an orbit indicating it came
from outside. Subsequently named 'Oumuamua, the visitor appears to have
a composition and shape unlike anything we have seen, leading to
discredited claims it was an alien spaceship. Two years later, Comet 2I/Borisov turned up and was found to be much more similar to Solar
System comets, although its orbit clearly marked it as interstellar.
We donrCOt yet have those sorts of details of the new object,
provisionally named A11pl3Z, or even whether it is a comet or asteroid,
but we know it is unlike the others in one important way: its orbit.
A11pl3Z is currently slightly inside the orbit of Jupiter, but on almost exactly the opposite side of the Sun, so it has not been affected by the
giant planetrCOs gravity.
First detected by the ATLAS sky survey on July 1, A11pl3Z was announced
on BlueSky by astronomy student K Ly with the handle astrafoxen. The
discovery set off a scramble by other observatories to see if they had
images of it that they had overlooked, which could help refine its orbit.
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It turned out ATLAS itself had records from June 25-28, and once
alerted, the Zwicky Transient Facility came up with data from June 14-21.
A11pl3Z seen by Deep Random Survey, Chile. The telescope is tracking the intruder, so the stars move and look stretched in 600-second exposures.
Image Credit: K Ly (astrafoxen)/Deep Random Survey
Orbits are measured by their eccentricity (e). Those bound to the
gravity well of a larger object have e values between zero (perfectly circular) and fractionally below 1 (extremely elongated like long-period comets). An eccentricity greater than 1 means an object is a one-time
visitor to the Solar System that wonrCOt be back.
'Oumuamua had an eccentricity of 1.20, and initial estimates were
somewhat lower, leading to some claims werCOd just mismeasured an orbit
that was a tiny bit below 1, and therefore not interstellar at all.
Comets or asteroids with eccentricities of less than one can be thrown
out of the Solar System by encounters with giant planets, so it also
took a while to check 'Oumuamua hadnrCOt only been recently boosted to an
e value greater than 1, after a lifetime spent orbiting the Sun.
A11pl3Z never left room for such doubt, its orbital eccentricity was
initially thought to be more than 10, and is currently estimated to be
above 6, Further change is possible, but itrCOs still more than double Borisov; werCOre definitely seeing something unlike any previous visitor.
People who have seen too many science fiction disaster movies neednrCOt
worry. A11pl3ZrCOs trajectory will never bring it within 50 million
kilometers (31 million miles) of EarthrCOs orbit, let alone Earth itself.
ThererCOs some uncertainty as to whether A11pl3Z will pass inside the
orbit of Mars (see image at top) at closest approach, expected in
October, or just outside it.
At magnitude 17.2, A11pl3Z is currently too faint for backyard
telescopes to detect, but that will change as it gets closer,
particularly if it turns out to be a comet. Annoyingly, however, the
closest approach will occur when Earth is worst positioned to see it, on
the opposite side of the Sun.
ORIGINALLY PUBLISHED
8 hours ago
ARTICLE POSTED IN
space-iconSpace and Physics
space-iconAstronomy
tag
comet,
Astronomy,
oumuamua,
interstellar visitor,
A11pl3
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