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<h3>Learning Objective</h3>
<ul>
<li>Recall that excited-state nitrogen dioxide is responsible for the glow observed as space shuttles re-enter Earth’s atmosphere.</li>
</ul>
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<h3>Key Points</h3>
<ul>
<li>When space shuttles return from space, there is often a phenomenon observed as they begin to re-enter the Earth’s atmosphere: a glow, especially around the tail end of the shuttle, is usually seen.</li>
<li>The glow around the space shuttle is due to excited-state nitrogen dioxide returning to its ground state and emitting photons or light; the excited-state nitrogen dioxide forms from nitric oxide (found on the surface of the space shuttle) and atomic oxygen (found in the atmosphere).</li>
<li>Atomic oxygen forms from the interaction of the sun’s high-energy light with molecular oxygen; the light has sufficient <a data-lesson="energy" data-subject="chemistry" data-tutorial="thermochemistry" href="https://app.ulearngo.com/chemistry/thermochemistry/energy">energy</a> to break the oxygen-oxygen bond in diatomic oxygen, producing single oxygen <a data-lesson="chemical-formulas" data-subject="chemistry" data-tutorial="atoms-molecules-ions" href="https://app.ulearngo.com/chemistry/atoms-molecules-ions/chemical-formulas">atoms</a> (O<sub>2</sub> goes to O).</li>
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<h3>Terms</h3>
<ul>
<li><strong>ground state:</strong> the lowest energy state of a particle or system of particles</li>
<li><strong>excited state:</strong> any state of a particle (often an electron) or system of <a data-lesson="the-kinetic-theory-of-gases" data-subject="chemistry" data-tutorial="states-of-matter" href="https://app.ulearngo.com/chemistry/states-of-matter/the-kinetic-theory-of-gases">particles</a> that has a higher energy than that of its ground state</li>
</ul>
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<p>When space shuttles return from space and being to re-enter the Earth’s atmosphere, a glow, especially around the tail end of the shuttle, can often be observed. This phenomenon has to do with the <a data-lesson="composition" data-subject="chemistry" data-tutorial="quantitative-aspects-chemical-change" href="https://app.ulearngo.com/chemistry/quantitative-aspects-chemical-change/composition">composition</a> of the atmosphere at these altitudes and the lack of shielding from the sun.</p>
<div class="wp-caption alignnone" style="width: 680px"><img alt="Shuttle glow: When atomic oxygen from the high atmosphere combines with nitric oxide on the surface of the space shuttle, the resulting excited nitrogen dioxide returns to the ground state emitting an apparent glow." height="447" src="https://data.ulearngo.com/assets/295b3162-cf7c-478c-bcf1-6c3763a16b0d" width="680"/><p class="wp-caption-text"><b>Shuttle glow</b>: When atomic oxygen from the high atmosphere combines with nitric oxide on the surface of the space shuttle, the resulting excited nitrogen dioxide returns to the ground state emitting an apparent glow.</p></div>
<h2>Where Does the Glow Come From?</h2>
<p>You may have heard of the <a data-lesson="polar-ozone-holes" data-subject="chemistry" data-tutorial="chemistry-real-world" href="https://app.ulearngo.com/chemistry/chemistry-real-world/polar-ozone-holes">ozone</a> layer, which protects the Earth from ultraviolet radiation. This protection is not present higher up in the atmosphere, however, where the high-energy light from the sun interacts with molecular oxygen, breaking it apart into atomic oxygen. This highly-reactive <a data-lesson="amphiprotic-species" data-subject="chemistry" data-tutorial="acid-base-equilibria" href="https://app.ulearngo.com/chemistry/acid-base-equilibria/amphiprotic-species">species</a> interacts with almost any molecule with which it comes in contact.</p>
<p>The lining of the space shuttle is no exception; specifically, the glow on the space shuttle forms when atomic oxygen reacts with the nitric oxide (NO) on the exterior of the shuttle. The origin of the NO is unclear, although it may be collected from the atmosphere or be a byproduct of the <a data-lesson="fuel-cells" data-subject="chemistry" data-tutorial="electrochemistry" href="https://app.ulearngo.com/chemistry/electrochemistry/fuel-cells">fuel</a> consumption from the shuttle thrusters. This interaction produces NO<sub>2</sub> according to the equation:</p>
<p>\(O+NO\rightarrow NO_2^*\rightarrow NO_2+light\)</p>
<p>where NO<sub>2</sub>* represents the excited state of <a data-lesson="orbital-shapes-and-valence-electrons" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/orbital-shapes-and-valence-electrons">electrons</a> in NO<sub>2</sub>. It is the relaxation of these electrons from the excited state back to the ground state that produces the glow that is visible around the space shuttle (see the concept about the emission spectra for more information).</p>

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Glow of Space Shuttles

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Glow of Space Shuttles

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