Sky & Telescope - December 2024 - 6

K2-18B ILLUSTRATION: ESA / HUBBLE / M. KORNMESSER
FROM OUR READERS
Life
Beyond
Earth
life here, it seems highly unlikely that,
among the 1 to 2 trillion galaxies in
our universe, that the same thing didn't
happen somewhere else. Numbers alone
would overwhelmingly argue for other
life to exist among the vastness in which
we are only a speck of dust.
Mark S. Donnell
Silver City, New Mexico
I just read " Our Fundamental Ignorance "
by Edward Zanders (S&T: July
2024, p. 84), and I found the article
fascinating. I have been interested in the
possibility of life existing elsewhere in
the universe for more than 60 years. To
this end, I recently went back to college
and studied both organic chemistry and
biochemistry. As a result of studying
these subjects, I became convinced that
carbon was the only possible element
that could be the basis of life. Carbon
has the proper abundance, valence, bond
strength, and electronegativity necessary
to assemble the mega-molecules needed
for life to exist. I would be very interested
in Zanders' thoughts and opinion
on this aspect of potential extraterrestrial
life.
Patrick Donnelly
Morgan Hill, California
"
Edward Zanders replies: You have
highlighted a key topic in astrobiology,
namely the chemical composition
of organisms that might be detected
elsewhere. In principle, we should avoid
assuming that just because our life is based
Championing Chandra
David Dickinson's " Chandra Observatory
Faces Premature End " (S&T: Aug.
2024, p. 10) includes an image of the
Crab Nebula (M1). Much of the data in
this image are from one of my Chandra
observations, and I was pleased to see
the image in Sky & Telescope. It shows
the central pulsar and circular flow of
high-energy electrons and is an excellent
example of the value of arcsecond
resolution in X-ray.
6
DECEMBER 2024 * SKY & TELESCOPE
on carbon, all other life must be as well.
In practice, however, our detailed knowledge
of the chemical elements and their
compounds makes it difficult, as you have
pointed out, to see how alternatives to carbon
could provide the necessary structures
and reactivity for making large molecules
with biological functions.
There are plenty of elements - silicon,
for example - that could be incorporated
into bioactive molecules, but not as a complete
replacement for carbon. Otherwise,
since silicon tends to form mineral-like
structures in conjunction with oxygen, you
could end up with the unlikely scenario of
living rocks. So given the current knowledge,
it's hard to see how life could exist
without a foundation in carbon chemistry.
I enjoyed reading Edward Zanders' article
regarding the origins of life on Earth
and its possible exclusivity. One idea that
he didn't mention is that regardless of
whether we believe that life originated
spontaneously on Earth, or whether
the beginnings were dropped here by a
passing comet or asteroid, or whether
an unknown omnipotent power started
Chandra is a unique resource for
astronomy because of its mirrors: a set
of four nested pairs of grazing-incidence
reflectors, built to have 0.5-arcsecond
resolution and large enough to collect
useful signals from faint sources. It is
difficult enough to build mirrors that
will focus X-rays, but to build a set that
brings the X-rays to such a sharp focus
as Chandra does was a real challenge.
The mirrors are the creation of Leon
van Speybroeck (1935-2002). He was
I enjoyed reading Edward Zanders' article
about our basic inability to say with
certainty that life exists beyond Earth.
But rather than wondering how likely
it is that life does exist beyond Earth, it
may be worth considering how likely it
is that life doesn't exist anywhere else.
And in that vein, I have created an analogy.
Imagine that on some beach somewhere
on Earth there is one single grain
of sand, and only one, that can talk. To
me, that's about as likely as Earth being
the only planet in the universe with life.
Jerry O'Shaughnessy
Vienna, Virginia
Edward Zanders has a PhD in biochemistry
and decades of life-science experience,
but his outstanding quality is his
mastery of the pen. In this marvelous
article, he invites us to take a step or
two backwards, distancing ourselves
a moment from the daily commotion
of this data-cluttered activity we call
science and delving into the profound
meaning of our existence.
Thank you, Edward Zanders, and
whatever you might do, I beseech you
not to let your noble quill run dry.
Patrick Kavanagh
Naucalpan, Mexico
smart, conscientious, and precise. The
mirror array was his baby. He designed
it and followed every step of the
manufacturing, testing, calibration, and
installation. I quietly thank van Speybroeck
every time I see an interesting
new object pop up in a Chandra image.
Indeed, the mirrors have given us 25
years of beautiful astronomical images.
Chandra's sub-arcsecond resolution
is an order of magnitude better
than that of other existing X-ray
Sky & Telescope - December 2024

Table of Contents for the Digital Edition of Sky & Telescope - December 2024
