Why there is so little breathable oxygen in space?

NASA,ESA, M. Robberto (STSI/ESA) and the Hubble Space Telescope Orion Treasury Project Team The Orion Nebula is one of only two interstellar clouds where astronomers have seen molecular oxygen.
NASA,ESA, M. Robberto (STSI/ESA) and the Hubble Space Telescope Orion Treasury Project Team
The Orion Nebula is one of only two interstellar clouds where astronomers have seen molecular oxygen.

science_equal_rgb_150w

News Science AAAS  By May 5, 2015

Μπορεί να το αναπνέουμε κάθε λεπτό, αλλά στο διάστημα δεν βρίσκεται σχεδόν καθόλου μοριακό οξυγόνο. Το 1998, η NASA εκτόξευσε δορυφόρο με την προσδοκία ότι θα έβρισκε αρκετή ποσότητα οξυγόνου, κάτι το οποίο δεν συνέβει και οι επιστήμονες θεωρώντας ότι είχε υποστεί βλάβη στα όργανα μέτρησης, τον κατεύθυναν πίσω στην γή. Στις μέρες μας, ένα επίγειο πείραμα αποκάλυψε γιατί το απαιραίτητο για τη ζωή μόριο, είναι τόσο σπάνιο στο σύμπαν: η στενή προσκόλληση των ατόμων του με την αστρόσκονη, εμποδίζει την μεταξύ τους αλληλεπίδραση, η οποία θα οδηγούσε στον σχηματισμό μοριακού οξυγόνου. Η ανακάλυψη αναμένεται να αποφέρει επίγνωση των χημικών συνθηκών που επικρατούν κατά την δημιουργία αστέρων και πλανητών._Π.Δ.Λιβάς

You breathe it every minute, but there’s hardly any molecular oxygen—otherwise known as O2—in space. In 1998, NASA even launched a satellite that was supposed to find lots of molecular oxygen but never did—except when scientists, worried that the instrument was faulty, aimed it at Earth. Now, a ground-based experiment has revealed why this life-giving molecule is so rare in the cosmos: because oxygen atoms cling tightly to stardust, preventing them from joining together to form oxygen molecules. The discovery should yield insight into the chemical conditions that prevail when stars and planets arise.

Oxygen is the third most common element in the universe, after hydrogen and helium, and in the 1970s astronomers predicted that molecular oxygen would be the third most common interstellar molecule, after molecular hydrogen (H2) and carbon monoxide (CO). It obviously isn’t. In fact, astronomers have detected interstellar molecular oxygen in only two places: the Orion Nebula and the Rho Ophiuchi cloud. But even there the molecule is much rarer than theory predicts. For example, hydrogen molecules in the Orion Nebula outnumber oxygen molecules a million to one.

To explain the scarcity, astronomers recently proposed that oxygen atoms bind tightly to the dust particles that pepper space clouds. «Everybody knows that the binding energy of atomic oxygen is very important,» says Jiao He, an experimental astrophysicist at Syracuse University in New York. «But there was no experimental measurement of this parameter.»

Now, He and his colleagues have measured this number. The scientists heated two types of solids that make up interstellar dust grains—water ice and silicate—to see how readily oxygen atoms escape. As they recently reported in The Astrophysical Journal, the binding energy of oxygen is more than twice what scientists had calculated decades ago: 0.14 electron volts for water ice and 0.16 electron volts for silicate. That’s high enough to keep oxygen atoms stuck to stardust without the minimal heat of cold interstellar clouds dislodging them. The Orion Nebula may owe its small quantity of molecular oxygen to a shock wave that ripped atoms from the dust grains; Earth’s air abounds with oxygen because trees and other plants put it there.

«It’s a very valuable measurement,» says Gary Melnick, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who recently predicted a binding energy about that high. «It explains a lot.»

Oxygen atoms that float away from interstellar dust grains can join to make molecular oxygen. But when they stay stuck to the grains, hydrogen atoms combine with the oxygen to create water ice (H2O) instead. The water can then become part of asteroids, comets, and planets, setting the stage for the creation of life.

Paul Goldsmith, an astronomer at the Jet Propulsion Laboratory in Pasadena, California, spent more than a quarter-century seeking interstellar molecular oxygen before finally succeeding when Europe’s Herschel Space Observatory examined the Orion Nebula in 2010 and detected the elusive molecule. «I may have been misguided in spending so many years searching for it, but in a way, with this laboratory data and all the Herschel data, we can really say well, we do understand it now.”

 

Provided by Science AAAS

Reference paper

Jiao He et al. 2015 ApJ 801 120 doi:10.1088/0004-637X/801/2/120

 

•••

 

 

 

Σχολιάστε

Εισάγετε τα παρακάτω στοιχεία ή επιλέξτε ένα εικονίδιο για να συνδεθείτε:

Λογότυπο WordPress.com

Σχολιάζετε χρησιμοποιώντας τον λογαριασμό WordPress.com. Αποσύνδεση / Αλλαγή )

Φωτογραφία Twitter

Σχολιάζετε χρησιμοποιώντας τον λογαριασμό Twitter. Αποσύνδεση / Αλλαγή )

Φωτογραφία Facebook

Σχολιάζετε χρησιμοποιώντας τον λογαριασμό Facebook. Αποσύνδεση / Αλλαγή )

Φωτογραφία Google+

Σχολιάζετε χρησιμοποιώντας τον λογαριασμό Google+. Αποσύνδεση / Αλλαγή )

Σύνδεση με %s