Next Horizons?

Dr Paul A Daniels, Guildford Astronomical Society

New Horizons – Pluto

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• Launched on 19th Jan 2006• Orbits 39.5 AU from Sun (1 AU is average Earth-Sun distance)

• Journey of 3,463 days = 9.48 years• 4,760,000,000 km journey (~3 billion miles)• Pluto flyby on 14th Jul 2015 at 12,500 km• 33.39 AU = 4.5 light-hours from Sun• Where next?

New Horizons – 2014 MU69

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• Discovered 26th Jun 2014 by HST• Magnitude +26• Orbits 44.2 AU from Sun, Period 293 years• Low inclination and eccentricity – classic KBO• Estimated diameter 30-45 km• Flyby on either 31st Dec 2018 or 1st Jan 2019• 43.4 AU from Sun at flyby• Where Next?

To Infinity and Beyond?

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• Where would we like to go?– Nearest star!– ‘Interesting’ star!!– Earth-like exoplanet!!!– Across the galaxy!!!!– Another galaxy!!!!!

• Can we?

To Infinity and Beyond?

5 Speed of light, c = 1 ly/yr

Destination Distance, d (ly) Time, t (yr) Speed, v (ly/yr)Pluto 0.00063 0.035 0.036

Proxima Centauri 4.24 2.866 2.959

Vega 24.04 6.825 7.045

Kepler-452b 1,400 52.081 53.763

Across Galaxy 100,000 440.162 454.378

Andromeda Galaxy 2,500,000 2,200.812 2,271.888

Destination Distance, d (ly) Time, t (yr)Pluto 0.00063 0.035

Proxima Centauri 4.24 2.866

Vega 24.04 6.825

Kepler-452b 1,400 52.081

Across Galaxy 100,000 440.162

Andromeda Galaxy 2,500,000 2,200.812

Destination Distance, d (ly)Pluto 0.00063

Proxima Centauri 4.24

Vega 24.04

Kepler-452b 1,400

Across Galaxy 100,000

Andromeda Galaxy 2,500,000

𝑑=12 𝑎𝑡

2𝑡=√2𝑑/𝑎𝑣=𝑎𝑡

• Let’s assume we can maintain a continuous acceleration of 1g = 9.81 m/s2 = 1.0323 ly/yr2

Travelling Relatively

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• Special relativity becomes important!

Time on rocketMass of rocket

𝛾=1

√1−(𝑣𝑐 )2

Travelling Relatively – Flyby!

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Destination Distance,d (ly)Time on

Earth, t (yr)Time on

Rocket, T (yr)Speed at Destination,v (ly/yr)

Pluto 0.00063 0.035 0.035 0.03603439122399

Proxima Centauri 4.24 5.120 2.296 0.98248961191519

Vega 24.04 24.992 3.827 0.99924629467535

Kepler-452b 1,400 1,400.971 7.736 0.99999975987502

Across Galaxy 100,000 100,000.971 11.879 0.99999999995287

Andromeda Galaxy 2,500,000 2,500,000.971 15.004 0.99999999999993

• Special relativity becomes important very quickly!

• But… this for a fast flyby – no slowing down!• Almost no time to view destination• Radio signals back to Earth highly red-shifted

Travelling Relatively – ‘Loiter’

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Destination Distance,d (ly)Time on

Earth, t (yr)Time on

Rocket, T (yr)

Pluto 0.00063 0.049 0.049

Proxima Centauri 4.24 5.869 3.545

Vega 24.04 25.909 6.380

Kepler-452b 1,400 1,401.940 14.127

Across Galaxy 100,000 100,001.942 22.413

Andromeda Galaxy 2,500,000 2,500,001.942 28.663

• Suppose we want to slow down to arrive at our destination at low speed?

• This is just ‘fiddling with numbers’ – what about the engine and fuel?

Travelling Relatively – Engine

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• Consider our options…– Chemical fuel– Nuclear fuel– Matter/Anti-Matter Annihilation– Gamma-ray Lasers (Grazers)– Star-Trek

• Warp drives• Wormholes• Black-hole slingshots

Travelling Relatively

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Destination Distance,d (ly)Fuel Mass perkg of Payload

Pluto 0.00063 0.05 kg

Proxima Centauri 4.24 37.52 kg

Vega 24.04 713.16 kg

Kepler-452b 1,400 2,085.13 tonnes

Across Galaxy 100,000 10,609,412.00 tonnes

Andromeda Galaxy 2,500,000 6,630,635,300.00 tonnes

• Assume we can convert matter to energy with 100% efficiency!

• How much matter do we need?

Travelling Relatively

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• Engine/Fuel not possible!– Wait for Star Trek solution?

• Slower travel possible (<1g)– Robotic Missions Only?– How many human generations?

• Shielding is an issue!– Interstellar dust– Cosmic Microwave Background

• Returning signals to Earth– Size of dish and power required– Delay between departure and signals returned!

𝑐=𝑠𝑝𝑒𝑒𝑑𝑜𝑓 h𝑙𝑖𝑔 𝑡 Inspired by ‘The Relativistic Rocket’

http://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/rocket.html