Washington: More than four decades after beginning its epic journey, NASA's Voyager 2 spacecraft has crossed the elusive boundary that marks the edge of the Sun's realm and the start of interstellar space, scientists have announced.
According to the researchers at the University of Iowa in the US, Voyager 2 has entered the interstellar medium (ISM), the region of space outside the bubble-shaped boundary produced by wind streaming outward from the Sun.
This makes Voyager 2 the second human-made object to journey out of the Sun's influence, following the US space agency's Voyager 1's solar exit in 2012.
The study, published in the journal Nature Astronomy, confirmed Voyager 2's passage on November 5, 2018, into the ISM by noting a definitive jump in plasma density detected by a plasma wave instrument on the spacecraft.
The marked increase in plasma density is evidence of Voyager 2 journeying from the hot, lower-density plasma characteristic of the solar wind to the cool, higher-density plasma of interstellar space, the researchers said.
It is also similar to the plasma density jump experienced by Voyager 1 when it crossed into interstellar space, they said.
"In a historical sense, the old idea that the solar wind will just be gradually whittled away as you go further into interstellar space is simply not true," said Professor Don Gurnett from the University of Iowa, and corresponding author on the study.
"We show with Voyager 2 -- and previously with Voyager 1 -- that there's a distinct boundary out there. It's just astonishing how fluids, including plasmas, form boundaries," Gurnett said.
Voyager 2's entry into the ISM occurred at 119.7 astronomical units (AU), or more than 11 billion miles from the Sun. Voyager 1 passed into the ISM at 122.6 AU.
The spacecraft were launched within weeks of each other by NASA in 1977, with different mission goals and trajectories through space. Yet they crossed into the ISM at basically the same distances from the Sun.
That gives valuable clues to the structure of the heliosphere -- the bubble, shaped much like a wind sock, created by the Sun's wind as it extends to the boundary of the solar system, the researchers said.
"It implies that the heliosphere is symmetric, at least at the two points where the Voyager spacecraft crossed," said Bill Kurth, University of Iowa research scientist and a co-author on the study.
"That says that these two points on the surface are almost at the same distance," Kurth said. "There's almost a spherical front to this. It's like a blunt bullet," Gurnett added.
Data from the instrument on Voyager 2 also gives additional clues to the thickness of the heliosheath, the outer region of the heliosphere and the point where the solar wind piles up against the approaching wind in interstellar space, which Gurnett likens to the effect of a snowplow on a city street.
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Jaipur, Mar 28: Young Riyan Parag showed why he is considered a precocious talent as he struck a stunning 84 not out off 45 balls to set up a 12-run win for Rajasthan Royals against Delhi Capitals in their IPL match here on Thursday.
Sent in to bat, RR were reduced to 36 for 3 in the eighth over but the 22-year-old Parag single-handedly took the home side to 185 for 5 with a magnificent unbeaten knock studded with seven fours and six sixes.
Parag, who was promoted to number 4 by the team management this season and made 43 in the previous match, took 25 runs off veteran South African pacer Anrich Nortje with scores of 4, 4, 6, 4, 6, 1 in the final over to hit his highest T20 score.
Chasing 186 for a win, DC could only manage 173 for 5 in 20 overs though South African youngster Tristan Stubbs (44 not out off 23 balls) kept them in the hunt till the final over from which they needed 17 runs.
Avesh Khan conceded just four runs to help RR win their second consecutive match.
South African pacer Nandre Burger and Yuzvendra Chahal took two wickets apiece to also contribute in the RR win.
"Definitely disappointed. The best thing to do from here is to learn from it. The bowlers did well through the 15-16 overs. But the batters did well at the death, hopefully we do better in the next game," DC skipper Rishabh Pant said.
DC were reduced to 34 for 2 in the fourth over with Burger taking two wickets in three balls in a fine display of fast bowling.
Burger, who was brought in as Impact Sub for Shimron Hetmyer, dismissed opener Mitchell Marsh (23 off 12 balls) and Ricky Bhui (0) in the fourth over.
DC captain Rishabh Pant came out to bat at the fall of Bhui's wicket and along with senior batter David Warner built the innings without taking too much risk. Delhi were 89 for 2 at the halfway stage.
Warner was the more aggressive one as he got the boundaries to keep DC in the hunt. The senior Australian batter fell one run short of his fifty courtesy a brilliant diving catch by Sandeep Sharma off the bowling of Avesh in the 12th over.
Warner and Pant were involved in a crucial 67-run partnership for the third wicket.
Playing in his 100th IPL match and 14 months after a horrible car crash, Pant tried to build the innings with occasional boundaries. But he got out for a 26-ball 28 as Chahal induced a faint lower edge for Sanju Samson to do the rest behind the stumps in the 14th over.
The asking rate shot up to more than 13 runs an over and DC needed 66 from the last five overs.
Stubbs kept DC in the game with two consecutive sixes off Ravichandran Ashwin in the 17th over, but in the end the Delhi side were short by 12 runs.
They needed 34 runs from the final two overs which they could not get. It was DC's second consecutive loss.
Earlier, Parag shared 54 and 52 runs respectively with Ravichandran Ashwin (29) and Dhruv Jurel (20) after RR made a shaky start.
Royals captain Samson struck three consecutive boundaries in the fourth over bowled by pacer Mukesh Kumar before nicking a Khaleel Ahmed delivery two overs later to Pant to get out for 15.
RR were 30 for 2 by then as Mukesh had given DC their first breakthrough with the wicket of Yashasvi Jaiswal (5).
The Royals were in more trouble after wrist spinner Kuldeep Yadav literally forced his captain Pant to take a review, which later proved to be successful, to dismiss Englishman Jos Buttler for an LBW decision.
Ashwin came out to bat at number five and he lofted a Kuldeep delivery for a six to help RR reach 58 for 3 at halfway stage. He gave Nortje even a harsher treatment with two sixes in the next over that yielded 15 runs.
Ashwin, however, holed out to Tristan Stubbs near the boundary ropes for a 19-ball 29.
Parag then made his presence felt, striking two boundaries and a six off Ahmed to take RR past 100 in the 15th over.