Also known as TYC
6859-1332-1, AC-24 2833-183, GCTP 4338, GJ 729, HIP 92403, LHS 3414, V1216
Sagittarii, Proxima Sagittarii
From the very beginning of the scientific
age, mankind’s explorations of the Heavens, as well as our more recent first
steps in the physical exploration of them, have been largely motivated by the
quite understandable quest for life beyond our own planet. It certainly
provided much early impetus for the painstaking telescopic reconnaissance of
the solar system from Galileo all the way to Sputnik. Always the hope lay just
under the surface (and occasionally right atop that surface) of discovering
some sure sign of life on the Moon, Mars, Venus, or even Mercury; whether it be
lunar cities (Gruithuisen), Martian canal-builders (Lowell), Venusian swamp
monsters (Arrhenius), to swarms of lunar insects (Pickering), or yet more
ultimately improbable ideas.
The Canals of Mars, as envisaged by Percival Lowell
Even
in the Space Age, the Search for Life has generally been at the forefront of
our extraterrestrial endeavors. The Viking landers were specifically designed
to look for telltale signs of organic processes on the Martian surface. The
Pioneer, Voyager, Galileo, and Cassini missions all had the identification of
possible biospheres elsewhere among the outer planets on their agendas. Even
when not formally an objective, the first question always asked (at least by
the public) when a new world had been revealed by a visiting spacecraft was
invariably “Is there life?”
This obsessive desire to answer the
question “Are we alone?” has continued right into the now
technologically-enabled search for worlds outside of our own solar system – the
so-called “exoplanets”. The Kepler Space Telescope, which has revealed the
existence of literally thousands of new planetary systems, only rises to the
public consciousness when claims are made that the latest discovery may
possibly be an “Earthlike” world, with interest invariably falling off as the
“yes, but” qualifiers start coming out in the press releases.
Well. There can be no such hopes for the
next target on our list. For we have not so far in our observational journey
through the Solar Neighborhood come across such an inhospitable star, such an
implacably hostile environment to life as we know it, such a less desirable
piece of real estate as Ross 154.
In many respects, Ross 154 is yet another
commonplace red dwarf, similar in many respects to the five others we have thus
far tracked down. With 17% of the Sun’s mass and 0.38% of its luminosity, it is
a typical star of stellar class M3.5V. Its diameter of approximately 24% of the
Sun’s measurement is also no surprise. And as is so common among stars of this
classification, it is also a flare star. But what a flare star! They can occur
on Ross 154 as often as once every 48 hours, and can measure as much as 125,000
miles across (one-fifth of the star’s circumference). Their intensity increases
toward the blue end of the spectrum, and the star’s overall visual magnitude
can increase during such an episode by as much as 3 to 4 magnitudes. They are
even stronger in the ultraviolet wavelengths, and the associated X-ray
emissions are more than 10,000 times as strong as similar flare episodes on the
Sun. Just imagine the effects on a planet within the “habitable zone”, which
for Ross 154 is centered at approximately 0.022 AU out. Any potential biosphere
would be regularly sterilized. No, Ross 154 will be no place to search for
life.
Otherwise, Ross 154 differs in significant
ways from those we have previously tracked down. For one thing, it is
relatively young – perhaps not quite a billion years old. For another, it does
not possess any notable velocity relative to the Sun, and orbits the Milky
Way’s core entirely within the galaxy’s “thin disk” (see the section above on
Lalande 21185). The star’s orbital eccentricity is 0.052, which means its
distance from the center of the galaxy varies from 27,000 to 31,000 ly. (The
Sun’s orbit takes it from 25,000 to 28,000 ly from the galactic core.) At
present, Ross 154 and the Sun are gradually approaching each other, and will
continue to do so for the next 157,000 years (at which point they will be
separated by a little more than 6 light years). After that time, their
respective orbits will cause the two stars to move further and further apart
for the next 100 million years or so, by which time we will be separated by
thousands of light years. So, despite the similarity in orbits, it is sheer
coincidence that we are as close to Ross 154 as we currently are.
No companions of planetary or any other
nature have been either observed or suspected about Ross 154 which, given the
unfavorable conditions described above, is probably just as well.
Observing Ross 154
When
I first approached the task of tracking down Ross 154, I did so with not much
optimism. First of all, its location in the constellation Sagittarius did not
bode well. I imagined a Needle in a Haystack search for an anonymous point of
light amidst the rich star fields of the Summer Milky Way. Secondly, the star’s
southerly position of declination -23º 50’ 10” was not at all promising. (On
our list, only the impossible WISE 1541-2250 lay further south.) From my usual
observing site at Howard County’s Carrs Mill Park, the similarly situated M22
globular cluster (quite close to our search area, with a declination of -23º
54’ 12.2”) scarcely clears the tops of the trees in that direction. Add to that
the fact that I would have to contend with the light pollution from Washington,
D.C. in that direction, and it looked like uphill odds all the way.
But
Ross 154 did have a few items in its favor, which I thought might help in my
search. Its relatively bright magnitude (for a red dwarf) of 10.43 meant it
wasn’t (like DX Cancri) out of the question for my equipment. Next,
when I actually checked out its precise location in my Uranometria 2000.0 Deep Sky Atlas, I found to my relief that it was
nowhere near the dense star clouds that fill so much of Sagittarius. In fact,
it was smack in the middle of an area of that constellation so devoid of stars
that I feared I’d be facing the opposite problem – that of having no convenient
guide points from which to star hop.
But as it turned out, that last problem
turned out to be not so great an issue after all. As can be seen in the above star chart,
Ross 154’s position directly north of the Teapot’s handle makes a convenient
starting point for our search. Draw an imaginary line between 3rd magnitude
Lambda Sagittarii (the top of the Teapot) and 5th magnitude Nu Sagittarii (of
no particular asterism), and our target lies close to the left end of that
line. For a moment, concentrate on the star Nu Sagittarii (a.k.a., 32
Sagittarii, which is what I’ll be calling it from here on out, to avoid
confusion with a nearby 5th magnitude star which shares the “Nu” designation,
the two stars going by Nu1 and Nu2). This star is
traditionally taken to be the eye of the archer for which the constellation is
named. (In fact, its proper name, Ain al Rami, is Arabic for “Eye of the
Archer.”) Slowly scan eastward in the direction of Mu Sagittarii (see star chart just below this paragraph) until you come across another 5th magnitude star, 28 Sagittarii. This
particular star was the cause of much excitement among planetary scientists on
the night of July 2-3, 1989, when it was occulted by both Saturn and its
largest moon, Titan. This was, of course, many years before the Cassini
spacecraft gone into orbit about the ringed planet, so this was the scientific
community’s best opportunity to date to measure and determine the chemical
composition of the atmospheres of those two bodies. And of course it gave many
an amateur astronomer the thrill of a lifetime, observing the star pop out amidst
the rings as it traversed the Encke Gap and Cassini division.
Once
you identified and admired these two stars, imagine a line connecting the two.
Then further picture a roughly equilateral triangle extending southwards,
towards the Teapot’s Handle. At the third point of this triangle, we will find
our goal.
Here is where things will get difficult.
There are no stars in this region even close to naked eye visibility. In fact,
the brightest luminary in the vicinity is the paltry magnitude 9.3 star HD
174312 (see star chart below this paragraph).
This makes a neat little isosceles triangle with two nondescript 11th
magnitude stars (among the brightest lights around in this benighted region).
If you can spot this triangle, you will have no trouble at all capturing
magnitude 10.43 Ross 154.
On the opposite side of Ross 154 from this
triangle, you should be able to pick out a curious bow tie asterism of stars of
magnitudes averaging roughly 10.5. As you can see in the above star chart, our target is
pretty much at the midpoint between these two stellar groupings.
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