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earth's brothers are mars venus and

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mercury and their history informs our

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understanding of our own planet and its

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history and its future

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and so we go to mercury which is the

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smallest planet the planet closest to

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the sun the planet made out of the

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densest materials the planet

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subjected to the most extreme radiation

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and energetic particles from the sun

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because the processes that built mercury

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the processes that have governed how

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mercury evolves are the same processes

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it's the distance from the planet that's

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the most critical and we've been

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watching that distance get smaller and

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smaller in our trajectory projections

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as a result of all the maneuvers that

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have gone on before all of the solar

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sailing that we've accomplished so far

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so we are on target

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and we're now awaiting

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the propulsive event that will put us

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into orbit around mercury and make

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messenger the first spacecraft to orbit

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messenger has been

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traveling to this point for more than

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six and a half years

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we have flown by mercury three times

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and we're now approaching the point uh

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the most critical point in the mission

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when we fire our propulsion system to go

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we have been honing the trajectory as

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we've been flying

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just as we did for each of the mercury

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flybys the guidance and control and

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navigation teams have been using a

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process known as solar sailing

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where they

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can change the orientation of the

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spacecraft a small amount they can tilt

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the solar arrays relative to one another

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by a small amount and use sunlight

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the radiation pressure from the sun

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like the wind on the sails of a sailboat

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to make fine changes in the trajectory

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after we achieve orbit around mercury

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there'll be a commissioning phase

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there'll be a period

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almost three weeks long where we

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carefully check out every subsystem on

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the spacecraft we carefully check out

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every instrument on the spacecraft to

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make sure that they're functioning to

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make sure that in the thermal

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environment of mercury orbit that

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everything's behaving as expected

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one of the mysteries now a 20 year old

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mystery that we hope to solve uh with

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messenger is is the rice on mercury the

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planet closest to the sun the planet

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with one of

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the hottest surface temperatures and and

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the most extreme variation in

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temperature between day and night could

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ice be permanently deposited in cold