Fly-by missions: What is the Point When We Have the Technology to Go Into Orbit?

Andrew Coates, UCL

New Horizons’ fly-by of Pluto and its moons is the latest in a historic string of missions to objects in the solar system. But given that a fly-by lasts for just a short time, how much can we really get out of it? There’s no doubt that the mission will yield a great deal of interesting data, but surely more would be gained if the spacecraft could go into orbit for a number of days or actually land on the surface and take physical samples.

New Horizons is hugely important because it is giving us a first glimpse into the unseen world of a third class of objects in the Kuiper belt – the building blocks of the outer solar system, located beyond the terrestrial and gas-giant planets. Fly-bys such as this are very exciting as they provide just one chance for unique measurements at the target.

While we are only at the very first stage of exploring Pluto and its moons, the fly-by will provide the foundations for future missions. Indeed, a fly-by is the first in the classical four stages of solar-system exploration and is followed – in this order – by an orbiter, a lander and the return of a sample from a body (marked 1-4 in the table below).

Lessons from the past

The first fly-by was of our Moon, made in 1959 by the Russian Luna-1 spacecraft. And 50 years ago, nearly to the day (July 15), the US Mariner 4 made the first fly-by of Mars.

My generation was captivated by the historic fly-bys of the outer planets and some of their moons, and I’ve been lucky enough in my own career to have been involved in instrument teams for several historic fly-bys. These were the Giotto mission to comets Halley (1986) and Grigg-Skjellerup (1992), as well as several close “fly-by firsts” in the Saturn system with the Cassini mission (such as moons Titan, Enceladus, Rhea, Dione, Hyperion).

Flyby firsts. Author provided

The Giotto fly-by of comet Halley only lasted a few days, but our knowledge of comets was revolutionised by this encounter. One of several probes to explore Halley in the mid-1980s, Giotto had the widest and most capable set of instruments and passed closer to its target than any of its companions.

It found cometary jet activity, a surprisingly dark surface, hydrocarbons in a crust and a complex bow shock and tail formation mechanism. These discoveries are now being followed up by the Rosetta mission and Philae lander at comet 67P.

Artist’s impression of Giotto approaching a comet.
Mirecki/wikimedia, CC BY-SA

But the fact that fly-bys happen so quickly can also make them very stressful and difficult to manage. When we were monitoring the Giotto spacecraft, flying past Halley at 68.4 km/s, it suddenly started spinning off its axis after encountering a dust particle near its closest approach. Fortunately it was possible to stop the wobble.

Comet Wild 2 as seen from Stardust on January 2, 2004

There are many other examples where data have been rescued – including with New Horizons during its worrying glitch (now fixed) on July 4.


Be Sure to Catch the Supermoon Lunar Eclipse! [Video]

One of the most rare of lunar eclipse events will be happening on September 27th and 28th, depending on where you are in the world, and hopefully you will be lucky enough to be somewhere to see it live. Neither a supermoon or an eclipse are rare events, according to a very informative article over on the NASA website. Supermoons happen every year when the moon is at its perigee, or the part of its orbit around the earth when it is closest. On those nights, the moon looks 14% larger than normal because it is closer. Eclipses happen about twice per year, so they are also pretty common.

But a supermoon lunar eclipse happens rarely, once every few decades. The last one occurred in 1982 and the next one isn’t predicted until 2033.

Now that’s rare! So be sure to get outside on the 27th and catch this maybe-twice-in-a-lifetime event!

From the article, here are the details on when the supermoon eclipse will be visible:

The total eclipse will last one hour and 12 minutes, and will be visible to North and South America, Europe, Africa, and parts of West Asia and the eastern Pacific. Viewers can see the supermoon unmasked after nightfall. Earth’s shadow will begin to dim the supermoon slightly beginning at 8:11 p.m. EDT. A noticeable shadow will begin to fall on the moon at 9:07 p.m., and the total eclipse will start at 10:11 p.m.

There are more details in the great article on NASA’s website, and here is a fun & informative video that they put together about this super-rare event:


Source: – “NASA Scientist Sheds Light on Rare Sept. 27 Supermoon Eclipse

Video Credit: NASA’s Goddard Shorts HD podcast

Correction: The original version of this article had the incorrect month for the event, it is in fact happening on September 27th, 2015!


Why Does Saturn’s Moon Enceladus Wobble? Here’s the Amazing Answer

There has been some debate in the astronomical science community about Enceladus, one of Saturn’s moons that has been closely studied for over 7 years.  The debate has focused on whether Enceladus has a global ocean, or whether the observations of amazing geysers of water around the south pole of the moon mean that there was simply a small ocean concentrated there.

An excellent article on spills the beans. After all those years of observations, they report that the startling conclusion to this very hard problem is thus:

The smoking gun is the very slight wobble that Enceladus displays as it orbits Saturn. This unsteady motion is effectively the result of water sloshing around inside Enceladus, and could not appear if the moon were made of ice all the way to its core. Instead, the moon must contain a complete ocean layer, according to new research that relied on more than seven years of images taken by NASA’s Cassini space probe.

“This was a hard problem that required years of observations, and calculations involving a diverse collection of disciplines, but we are confident we finally got it right,” Peter Thomas, lead author of the new work and a Cassini imaging team member at Cornell University, said in a statement from the Cassini imaging team.

Thomas and his colleagues studied images of Enceladus to precisely measure changes in its rotation, then ran several simulations to determine how the interior of the moon would affect those wobbles.

The article explains how Thomas and his team painstakingly analyzed the available data to come to their stunning conclusion that there is a global ocean underneath a thin, icy crust:

“If the surface and core were rigidly connected, the core would provide so much dead weight the wobble would be far smaller than we observe it to be,” co-author Matthew Tiscareno, a Cassini participating scientist at the SETI Institute in California, said in the same statement.

“This proves that there must be a global layer of liquid separating the surface from the core.”

There are more mysteries to be solved regarding this amazing discovery, but for now you can read all of the details in the excellent article on


Source: – “An Ocean Flows Under Saturn’s Icy Moon Enceladus

Featured Photo Credit: NASA/JPL-Caltech/Space Science Institute

[Video] Watch as a Comet Zooms to its Death in the Sun

This awesome video shows the death of a comet as it speeds headlong into the Sun. Utterly fascinating to see its last moments, courtesy of


This video was captured by the Solar and Heliospheric Observatory (SOHO) spacecraft, which has a special camera that occludes the solar disk so that the Sun’s corona can be researched. It has also been used to discover thousands of comets, many known as Kreutz sungrazers, which “graze” the Sun by coming within 500,000 miles of its surface. Occasionally, one of these sungrazers will plow directly into the sun, vaporizing within seconds. SOHO can be accessed on the internet by amateur comet hunters and just passed the “3000 comets discovered” mark on September 13, 2015.

Source: – “Death-Diving Comet Plunges Into Sun | Video

Watch Tomorrow’s Solar Eclipse from Anywhere

If you can’t make it to Southern Africa to watch the solar eclipse tomorrow, you can catch it broadcast live from the Slooh Community Observatory, as reported in a detailed article on

A partial solar eclipse will darken the skies above southern Africa early Sunday (Sept. 13), and the entire world can watch the spectacle live online. Sunday’s eclipse will be visible to observers throughout South Africa, as well as people in the southern parts of Mozambique, Zambia, Zimbabwe and Madagascar. But wherever you are, you can view the eclipse live thanks to a free webcast hosted by the Slooh Community Observatory. The Slooh show begins at 12:30 a.m. EDT (0430 GMT) Sunday and can be viewed live on along with the observatory’s archive of night sky webcasts. It will run through 5 a.m. EDT (0900 GMT), with the time of maximum eclipse expected at 3 a.m. EDT (0700 GMT).

You can also watch the solar eclipse live on, courtesy of Slooh. The webcast will feature Slooh astronomer Bob Berman and solar researcher Lucie Green.

Ever wondered how it is that total solar eclipses can happen at all? The article answers that with this interesting factiod:

That total solar eclipses can occur at all is a strange accident of cosmic geometry. The sun is about 400 times wider than the moon, but it’s also 400 times farther from Earth, so the two objects are roughly the same size in Earth’s sky.

While partial solar eclipses are interesting events, total eclipses are more exciting both visually and scientifically, experts say.

“During a total solar eclipse, the moon is a near-perfect fit for the sun’s disk, so almost all of the corona is visible,” Jack Ireland, a solar physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a statement.

The corona is the sun’s thin atmosphere, which is ordinarily tough to observe because it gets lost in the overwhelming glare coming from the solar surface.

Therefore, total solar eclipses are the perfect opportunities for astronomers to study the sun’s corona.

Get all the facts on tomorrow’s eclipse in’s highly informative article.



Source: – “Watch Sunday’s Partial Solar Eclipse Live in Slooh Webcast

Photo Credit: Kali Morgan/