MU69 is among the smallest ob­jects and or­bits more than 4 bil­lion miles from the sun

New Straits Times - - Opinion -

THIS sum­mer, sci­en­tists criss­crossed two oceans, braved wind and cold and de­ployed two dozen tele­scopes — all for five blinks of starlight that lasted a sec­ond or less.

For the team work­ing with NASA’s New Hori­zons spacecraft, which made a spec­tac­u­lar flyby of Pluto two years ago, those smidgens of data pro­vide in­trigu­ing hints about the spacecraft’s next des­ti­na­tion, a dis­tant frozen world that is be­lieved to be a pris­tine, undis­turbed frag­ment from the ear­li­est days of the so­lar sys­tem.

New Hori­zons will fly past it on Jan 1, 2019. But, the ob­ject is so far away — 1 bil­lion miles be­yond Pluto — and so small — no more than 20 miles wide — that al­most noth­ing was known about it.

From the five blinks, ob­tained with ex­haust­ing ef­fort, sci­en­tists now know that it has an odd shape. In­stead of round like a ball it ap­pears to be more like a long, skinny potato — or maybe two ob­jects in close or­bit around each other, pos­si­bly even touch­ing.

“It’s like, wow, this is go­ing to be re­ally cool,” said Marc W. Buie, an as­tronomer at the South­west Re­search In­sti­tute in Boul­der, Colorado, who led the ob­ser­va­tions. “We don’t know what we’re go­ing to find.”

While Pluto is the big­gest ob­ject in the ring of icy de­bris be­yond Nep­tune known as the Kuiper belt, this ob­ject with the des­ig­na­tion 2014 MU69 is among the smallest. It or­bits more than 4 bil­lion miles (6.43 bil­lion km) from the sun, and it is like a time cap­sule, promis­ing clues about how the plan­ets formed.

Astronomers, us­ing the Hub­ble Space Tele­scope, first spied it three years ago as they searched for some­where for New Hori­zons to visit af­ter Pluto.

All Hub­ble could see was a slowly mov­ing speck of light — enough to cal­cu­late an or­bit and de­ter­mine that New Hori­zons could reach it. But, al­most every­thing else about MU69 was a mys­tery or a guess. Not even the largest, most pow­er­ful tele­scopes on Earth can see it at all.

The New Hori­zons sci­en­tists could, how­ever, learn more about it dur­ing a few chance mo­ments when a star in the night­sky mo­men­tar­ily van­ished be­cause MU69 passed in front of it.

From the dis­tance to MU69, its speed and how long the star winks out, astronomers can cal­cu­late the width of the ob­ject.

It turned out that a bo­nanza of three such events, known as oc­cul­ta­tions, were set to oc­cur within a two-month pe­riod this year, on June 3, July 10 and July 17, as MU69 passed in front of three dif­fer­ent stars.

Buie had been scram­bling to gather equip­ment and ob­servers, and on June 3, 50 team mem­bers turned 24 tele­scopes on two con­ti­nents, in Ar­gentina and South Africa, to the sky. The tele­scopes took more than 100,000 images of the star, wait­ing for MU69 to pass in front of it. But, the star never van­ished. The sci­en­tists had com­pletely missed the shadow.

“I was phys­i­cally and emo­tion­ally ex­hausted, psy­chi­cally dam­aged,” Buie said.

In late June and early July, Hub­ble made ad­di­tional ob­ser­va­tions of MU69 that re­fined the or­bit.

The July 10 oc­cul­ta­tion track mostly passed over the south­ern Pa­cific. This time, the New Hori­zons sci­en­tists took off from Christchurch, New Zealand, in Sofia, a NASA 747 equipped with an 8.2-foot-di­am­e­ter tele­scope. They headed north, to­ward Fiji, to in­ter­cept the shadow and re­turned 10 hours later.

Again, the star never disappeared. They had missed the op­por­tu­nity again. They im­me­di­ately headed back to Ar­gentina for one more try.

S. Alan Stern, the prin­ci­pal in­ves­ti­ga­tor of New Hori­zons, said he was con­fi­dent, with the ad­di­tional Hub­ble mea­sure­ments, that they would cap­ture the van­ish­ing of a star this time. But mis­sion man­agers also al­ways worry about the so-called un­known un­knowns. Per­haps some­thing unan­tic­i­pated in the Hub­ble data was de­ceiv­ing them about MU69’s po­si­tion.

The July 17 shadow was pre­dicted to pass over Co­modoro Ri­va­davia, a city along the At­lantic coast of South Amer­ica. Co­modoro’s nick­name is “the cap­i­tal of wind”. In the mid­dle of win­ter, the weather was also cold.

“It was a pretty in­tense event,” Stern said. “Your tele­scopes were shak­ing.”

At sev­eral ob­serv­ing sites, trac­tor-trailer trucks served as wind­breaks, as did con­trap­tions made of poles and can­vas. A high­way was shut for a cou­ple of hours so that the head­lights of cars and trucks would not spoil the ob­ser­va­tions. The skies were clear, and the time of the shadow, 12.50am, passed.

A few hours later, Amanda M. Zan­gari, a South­west Re­search In­sti­tute sci­en­tist on the New Hori­zons team, was star­ing blearily at her lap­top analysing the data from one of the tele­scopes.

In her ex­haus­tion, the data was not mak­ing sense to her. Then it hit her.

“I re­alised it didn’t make any sense, be­cause the oc­cul­ta­tion star was miss­ing,” she said.

Five tele­scopes, it turned out, had de­tected the star’s van­ish­ing for up to about a sec­ond.

The suc­cess also con­firmed that the Sofia ob­ser­va­tions a week ear­lier had barely missed the oc­cul­ta­tion and were close enough to the shadow to be use­ful. Pre­lim­i­nary anal­y­sis found no signs of dim­ming, in­di­cat­ing there are no clouds of de­bris in the neigh­bour­hood of MU69 that could im­peril New Hori­zons.

The five blinks es­tab­lished the odd shape. If it is one skinny potato, MU69 is no more than 32km long. If it is two spheres cir­cling each other, each is about 14.4km to 19.3km wide.

Many Kuiper belt ob­jects in this re­gion are bi­na­ries, al­though most are con­sid­er­ably larger than MU69. If one this small can be a bi­nary, that may change the un­der­stand­ing of how Kuiper belt ob­jects are formed.

Mis­sion man­agers can still tweak the flyby time of the New Hori­zons spacecraft by a cou­ple of hours. Ideally, they want to view the broad side of MU69 and op­ti­mise ge­om­e­try of track­ing sta­tions on Earth dur­ing the flyby.

“We’re work­ing through all those math­e­mat­i­cal is­sues,” Stern said.

An­other oc­cul­ta­tion is pos­si­ble in Au­gust next year. The sci­en­tists have not de­cided whether they will chase the shadow one more time. The writer is a science re­porter at The New York Times since 2000. He cov­ers chem­istry, ge­ol­ogy, solid state physics, nan­otech­nol­ogy, Pluto, plague and other sci­en­tific mis­cel­lany

Many Kuiper belt ob­jects in this re­gion are bi­na­ries, al­though most are con­sid­er­ably larger than MU69. If one this small can be a bi­nary, that may change the un­der­stand­ing of how Kuiper belt ob­jects are formed.


An artist’s im­pres­sion of Kuiper belt ob­ject 2014 MU69.

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