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Hello all,</div>
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Reminder that we will be joined by Emma Lovett tomorrow (Tuesday, April 29th) for our weekly PLS lecture.</div>
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Emma is available on Tuesday for one-on-one chats. You can sign up for a meeting <a href="https://docs.google.com/spreadsheets/d/1EOtC-I1iqS0pMM17Z-fdCSpwe-JNgNN-mbOYo95jgro/edit?usp=sharing" target="_blank" id="OWA8d66fb74-61a2-999b-dc93-66e1f5c61155" class="x_OWAAutoLink elementToProof" title="https://docs.google.com/spreadsheets/d/1EOtC-I1iqS0pMM17Z-fdCSpwe-JNgNN-mbOYo95jgro/edit?usp=sharing" rel="noopener noreferrer" data-linkindex="0" data-auth="NotApplicable" style="margin: 0px; text-align: left;">
here</a>.</div>
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More information is below in my previous email.</div>
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Best,</div>
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Isaac</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Isaac Narrett<br>
<b>Sent:</b> Thursday, April 24, 2025 9:47 AM<br>
<b>To:</b> planetary <planetary@mit.edu>; baps <baps@mit.edu>; mitexoplanets <mitexoplanets@mit.edu><br>
<b>Cc:</b> Lovett, Emma <elovett@bu.edu><br>
<b>Subject:</b> PLS April 29th - Emma Lovett</font>
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<div dir="ltr"><span style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">Hello all,</span>
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We’re excited to announce that next week’s planetary seminar will be given by Emma Lovett from Boston University. She will be joining to discuss her work on Europa's exosphere. Please join us on Tuesday April 29 at 12:30 PM in 54-517 or on Zoom. Lunch will
be provided and we encourage you to arrive a bit early to get food.</div>
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Emma is available on Tuesday for one-on-one chats. You can sign up for a meeting <a href="https://docs.google.com/spreadsheets/d/1EOtC-I1iqS0pMM17Z-fdCSpwe-JNgNN-mbOYo95jgro/edit?usp=sharing" id="LPlnk" class="x_OWAAutoLink" title="https://docs.google.com/spreadsheets/d/1EOtC-I1iqS0pMM17Z-fdCSpwe-JNgNN-mbOYo95jgro/edit?usp=sharing">
here</a>.</div>
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Talk details and Zoom information are below. Look forward to seeing you there!</div>
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-Isaac</div>
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<i>Ground-based Observations of Europa’s Alkali Exosphere during the Juno Flyby</i></div>
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Jupiter’s icy moon Europa is enveloped in gaseous sodium and potassium that resonantly scatters sunlight as optical emission lines. The High Resolution Echelle Spectrograph on the Keck 1 telescope has spatially mapped these alkalis contemporaneously with Juno’s
PJ45 flyby. Beyond 3 Europa radii, where emission becomes separable from bright surface reflectance, their extended radial profiles indicate atmospheric escape. This suggests alkalis are ejected from the ice by a high energy process— likely ion sputtering—
into an exosphere where initial energies are not appreciably dampened through collisions with the cold O2 atmosphere and icy surface. The neutral sodium cloud appears oval-shaped with remarkable symmetry east-west and north-south, a sign that incident plasma
has access to the majority of Europa’s surface, and effects of centrifugal latitude may be negligible at the time of observations. The Na column density is a few ×1010 atoms cm-2, and the Na/K ratio 27 ± 8 at 10 Europa radii, consistent with prior estimates.
However, this ratio decreases with distance despite sodium’s lower mass and lifetime against ionization. Doppler broadening in the resolved Na line profiles grows with tangent altitude from a few thousand Kelvin to >15,000 K by 25 Europa radii. Considering
the more than two-fold increase in Io’s Na loss at this time, brightness levels in good agreement with past data reinforce an interpretation that Europa is a net source of alkali atoms that ultimately derive from its subsurface brines or saline ocean.</div>
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Zoom link: <a href="https://mit.zoom.us/j/97275591700" target="_blank" id="OWAde5f716a-4653-703f-16e0-697708b2f4b3" class="x_OWAAutoLink" title="https://mit.zoom.us/j/97275591700" rel="noopener noreferrer" data-auth="NotApplicable" data-linkindex="1" style="margin:0px">
https://mit.zoom.us/j/97275591700</a></div>
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PW: 54100</div>
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