Ahead of today's second practice session, the air temperature is 21 degrees C, while the track temperature is 36 degrees.

Mercedes absolutely blitzed the opposition earlier, Lewis Hamilton, though only 0.315s ahead of his teammate, was 1.951s clear of third-placed Max Verstappen.

The Mercedes duo were on the soft tyres when they posted their best times however, while the Dutch youngster, like his teammate who finished the morning seventh, was on mediums.

Raikkonen was fourth, also on the mediums, while the highest placed supersoft runner was Kvyat down in ninth.

As ever, grip was an issue for a number of drivers, as was debris, with Sebastian Vettel and Romain Grosjean shedding bits of their cars.

Sergio Perez and Pascal Wehrlein watched the action from the sidelines, having handed their cars over to Alfonso Celis and Jordan King respectively. The Briton, in particular, did well, out-pacing teammate Esteban Ocon.

The lights go green and Wehrlein leads the way followed by the Haas duo, Gutierrez and Grosjean having a somewhat ignominious conclusion to this morning's session.

Gutierrez posts the first time of the afternoon, the Mexican crossing the line at 42.246. Teammate Grosjean subsequently posts 40.848 but this is soon beaten by Raikkonen (38.930).

Replay shows Alonso having a little bit of fun with Raikkonen, pushing the Finn much faster than he actually wants to go in his attempts to get past.

A 38.892 sees Vettel go quickest as Perez goes third, on his first flying lap of the weekend, ahead of Grosjean, Alonso and Hulkenberg.

A mistake at T1 destroys Hamilton's lap before it has even begun. He crosses the line at 2:14.071.

Kvyat goes third and Massa fourth, as the Mercedes duo trade fastest sector times.

Verstappen posts 38.541 to go quickest but is soon demoted when Rosberg (softs) posts 38.082 and Hamilton (medium) 38.394.

Ricciardo is given details of how both Ferrari drivers lost around 0.6s on their second flying laps. The Australian responds with a 38.675 to go fourth.

Ocon does well to escape the kitty litter at T18, the Frenchman losing the back end but managing to keep one rear wheel on the tarmac thus enabling his speedy exit.

As Rosberg says he lost some grip at the rear, Palmer runs wide in T19.

The Sauber duo are the last to post a time, Ericsson going 17th with a 41.034 and Nasr going 19th with a 41.833.

Twenty minutes into the session, Raikkonen makes the switch to supersofts. Currently sixth, 0.848s down on Rosberg, the Finn has a poor first sector. Meanwhile, Vettel joins him on track, the German also on the red-banded rubber.

While Raikkonen posts a PB in S2, he subsequently runs wide at T19 and is unable to improve.

Vettel has a stronger S1 but only posts a PB. He finally crosses the line at 38.178 to go second, having gone quickest in S3 despite a mistake in T19.

Hulkenberg, also on the supers, posts PBs in all three sectors, crossing the line at 38.508 to go fourth.

More and more drivers switch to the supers, among them Rosberg and Hamilton.

As Rosberg goes quickest in S2, Ricciardo goes quickest in S1. The German crosses the line at 37.358, with Ricciardo posting 37.552 moments later. Hamilton can only manage third (37.649).

Ricciardo's time demonstrates that Red Bull can give Mercedes a hard time here, while Ferrari looks to be under pressure from force India and Williams.

A 40.086 sees Ocon go eleventh, enough to give the French youngster a nosebleed.

Ricciardo reveals that his car was pulling to the right under braking, suggesting that there was even more to come from the Australian.

Alonso improves from 40.906 (21st) to eighth (38.801), just behind the Force India duo of Perez and Hulkenberg.

A 38.713 sees Button leapfrog his McLaren teammate to take eighth.

"Still too much understeer," complains Wehrlein, "in low, medium and high speeds".

As focus now appears to switch to longer runs, Rosberg remains quickest, ahead of Ricciardo, Hamilton, Vettel, Verstappen, Hulkenberg, Perez, Button, Alonso and Raikkonen.

Check out our Friday gallery from Austin, here.