{"id":29804,"date":"2022-02-25T08:48:02","date_gmt":"2022-02-25T08:48:02","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=105144"},"modified":"2022-02-25T09:05:10","modified_gmt":"2022-02-25T09:05:10","slug":"meet-the-scorching-exoplanet-thats-dark-as-charcoal-with-a-sapphire-sky","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/meet-the-scorching-exoplanet-thats-dark-as-charcoal-with-a-sapphire-sky\/","title":{"rendered":"Meet the scorching exoplanet that\u2019s dark as charcoal with a sapphire sky"},"content":{"rendered":"

<\/p>

By Lewis Dartnell\n \t\t<\/p>

Published: Friday, 25 February 2022 at 12:00 am<\/p>

\n\n

\u2009<\/span>HAT-P-7b (or Kepler-2b) is an exotic exoplanet<\/a>. Discovered in 2008, it has a radius greater than that of Jupiter<\/a> and an orbital plane so tilted relative to its star (108\u00b0) that it\u2019s nearly in a polar orbit.<\/p>\n

But what makes the planet truly exceptional is how hot it is.<\/p>\n

HAT-P-7b hugs its bright, A-class star so tightly that its orbit takes less than three days \u2013 it\u2019s over 20 times closer to its sun than Earth is to ours.<\/p>\n

Day-side temperatures on the planet are calculated to be regularly above 2,200\u00b0C \u2013 similar to many stars themselves.<\/p>\n

You may have heard of a type of exoplanet known as a hot Jupiter<\/a>. Well, fittingly, HAT-P-7b sits in a class of planet known as \u2018ultra-hot Jupiters\u2019.<\/p>\n

Read our guide to the 9 weirdest exoplanets<\/a>, or our interview with exoplanet hunter Niall Deacon<\/a>.<\/strong><\/em><\/p>\n

\""An\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
An artist\u2019s impression of the planet HAT-P-7b. Credit: University of Warwick\/Mark Garlick<\/span><\/figcaption><\/div>\n

It\u2019s also one of the darkest planets ever observed, with an albedo (surface reflection) of less than 0.03 \u2013 roughly that of a lump of charcoal.<\/p>\n

The planet is so black it absorbs more than 97% of visible light shining onto it.<\/p>\n

Chemical models of its atmosphere predict that on its slightly cooler night-side the crystalline aluminium oxide mineral \u2018corundum\u2019, the same substance as rubies and sapphires, condenses as clouds.<\/p>\n

The enormous heating has also inflated the planet\u2019s upper atmosphere into a puffy envelope and this, combined with the brightness of its sun, means that HAT-P-7b is an ideal target for studying with transmission spectroscopy<\/a>.<\/p>\n

\""Transmission\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Transmission spectroscopy splits the starlight passing through an exoplanet\u2019s atmosphere to reveal information about its chemical composition. Credit: Christine Daniloff\/MIT, Julien de Wit<\/span><\/figcaption><\/div>\n

In this technique, the starlight that passes through a planet\u2019s atmosphere is analysed to reveal information about the chemicals that have become imprinted on it.<\/p>\n

Aaron Bello-Arufe at the National Space Institute, part of the Technical University of Denmark, and his colleagues are the first team to analyse HAT-P-7b using transmission spectroscopy, and they\u2019ve discovered even more astonishing details.<\/p>\n

Observing HAT-P-7b passing its host star<\/strong><\/h2>\n

The astronomers used the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N), a high-resolution spectrograph on the 3.6m Telescopio Nazionale Galileo at the Roque de los Muchachos Observatory on La Palma in the Canary Islands.<\/p>\n

They observed a single transit of HAT-P-7b across its star on the night of 18 December 2020 and recorded the spectrum of light passing through its atmosphere.<\/p>\n

\""The\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
The radial velocity method of exoplanet detection looks for a shift in the spectrum of star light as a star wobbles due to the gravitational pull of an exoplanet in orbit around it. Credit: ESA<\/span><\/figcaption><\/div>\n

They reported detecting a whole host of elements including iron, calcium, magnesium, sodium and chromium \u2013 possibly titanium too.<\/p>\n

Bello-Arufe\u2019s work has marked HAT-P-7b out as one of the exoplanets with the greatest number of atomic species detected in its atmosphere.<\/p>\n

And this metal-laden air is testament to just how hot the planet is.<\/p>\n

But Bello-Arufe\u2019s team also discovered that the spectroscopic lines of these atmospheric atoms are significantly blue-shifted in their observations, revealing just how fast the atmosphere is churning in the heat.<\/p>\n

They calculated wind speeds of over 2km per second \u2013 some 7,200 km\/h \u2013 as the expanding day-side air rushes towards the cooler night-side.<\/p>\n

What\u2019s more, because different atomic species are expected at different altitudes, the team was able to construct a rough wind-speed profile.<\/p>\n

The next step, they say, would be to use emission spectroscopy to study the chemical composition of the day-side of the planet.<\/p>\n

Lewis Dartnell was reading <\/em>Mining the Ultra-Hot Skies of HAT-P-7b: Detection of a Profusion of Neutral and Ionized Species by Aaron Bello-Arufe et al. Read it online at: arxiv.org\/abs\/2112.03292<\/a>.<\/em><\/strong><\/p><\/body><\/html>\n

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